FINALLY! It's finished! =D
I'm very proud of this little guy here. Took me several weeks and a lot of calculation to properly determine, weight, size, capabilities, and loadout. The model itself was created in UnrealEd.

And now for the most importan part: the fluff that makes the world go round.
Enjoy! ^^

Name: Cougar
Category: light tank/Scout
Length: 5.98 m
Width: 2.88 m
Height: 2.30 m
Mass: 17.4 t
Crew: 3
Top Speed: 65 kph
Range: 700 km (@28 l/ 100 km)
Armor:
Basic armor: 50 mm 5083 Aluminum
Sides: + 60 mm perforated armor plates (bolted-on)
Front: + BDD "Brow" NERA armor module
Turret Front: + 20 mm HHA, 10 mm Borium Carbide, Polyurethane foam
Turret Sides: + 20 mm HHA, 10 mm Borium Carbide
Armament:
2 57 mm L/55 guns
1 40 mm automatic grenade launcher
1 7.62 mm MG-3
2x4 vehicular grenade launchers (smoke)
3+ IronFist hardkill turrets
2x2 mine-clearing harpoons/demolition rocketlaunchers


Overview:
What happens if you decide to create something that is supposed to not to fight but the remaining 95 percent of ground targets a foe can offer? You'll get something that dramatically differs from an MBT, but this does not mean that it can't stand up a good fight.
The Cougar light tank is a theoretical example of how a light tank could look like if you erase the Main Battle Tank from the equasion and focus on the rest, leaving defensive measures against MBTs as an option but not as a main goal.

Maneuverability:
The Cougar is very small (a bit longer than the M551 Sheridan, but not as tall), and therefore it's very light despite it's armor. At a weight of 17.4 metric tons and a chassis similar to a stretched M113 (whose suspension and tracks it uses to gain a high commonality of parts, and rhus makes logistics a lot easier), it produces 0.6859 g/cm² (9.79 psi), which means that it has little problems with soft ground. Additionally, it's small size is very useful in confined areas, such as cities, where it can weasel through the streets with ease.
In order to reduce the fuel consumption, the Cougar uses a very fuel-efficient diesel engine usually found in modern cargo trucks. At 350 HP, these engines can reduce the fuel consumption to far less than 30 l/100 km (8+ mpg) and still provide 65+ kph. An important feature is it's snorkel mounted as an extendable arm in the aft. With it, the Cougar is able to dive through rivers and small lakes, provided it's not deeper than 7 meters. If the Cougar is forced to dive deeper, it can be equipped with eternal oxygen tanks.

Protection:
The Cougar's basic chassis is made of 5083 aluminum, at 50 mm thickness, and is covered with spall liners on the inside. This protects it from anything with an AP value of less than 30 mm of RHA steel by default. Additionally, the sides are protected by 60 mm of perforated, laminar hardened steel plates bolted onto the hull to reduce the tensions caused by the tank's movement. In conjunction with the spall liners and the dampening effects of layered armor, the sides have an RHA equivalent of over 100 mm, enough to withstand even a vertical hit from a 30 mm APFSDS round. In order to protect the sides from HEAT rounds like the RPG-7, the Cougar also wears bar armor skirts on the side by default, and the inside of the tank is also partially filled with approx 100 mm of polyurethane foam, which has well-documented stopping power against the copper jets of a shaped charge like common RHA steel. Because of the large gap between the actual hull and the bar armor caused by the tracks of the tank (which are separated by the upper area of the gap by a thin aluminum plate), most incoming HEAT warheads will either be deformed, the fuze will be short-circuited, or the warhead's direction will be changed before it detonates, an effect which made the M113A3 Gavin, which uses the same system, immune to RPG-7 and AT-3 Sagger rounds.
The front is equipped with a huge plate of BDD "Bork" armor developed in russia. It is a NERA (non-explosive reactive armor) system made of RHA steel (perforated hardened plated in case of the Cougar), polyurethane, and mild steel plates. By itself, BDD armor has proven to be equivalent to 250 mm of RHA against HEAT and 120 mm against KE rounds, in conjunction with the basic 5083 armor and at least 200 mm of foam, it provides 150 mm against KE rounds and 480 mm against HEAT. Additional bar armor can be added to protect the tank against even larger HEAT rounds, or to minimize the damage done to the NERA system caused by smaller weapons like the RPG-7. With the engine located to the left of the driver compartment, and the gear and drivetrain in front of him, the driver gains an additional protection when the vehicle is shot at. This is already a proven concept on the israeli Merkava MBT, and saved a lot of lives on older designs like the M113 as well.
Unlike the glacis, the turret uses polyurethane foam as it's main defense against HEAT rounds. the basic 50 mm aluminum armor is covered by additional plates of borium carbide, which offers 4 times the protection as RHA, a thin 5 mm steel plate, and a set of spaced armor modules willed with foam. This combination provides a minimum of 110 mm of RHAe against KE rounds, and over 500 mm of RHAe against HEAT rounds. Additional bar armor can be applied.
For active protection, the Cougar has two grenade launcher arrays to create a smoke screen to conceal it's movement, and carries three turrets for the IronFist hardkill system, which automatically engages and destroys incoming ATGMs and large-bore penetrators. Two of these turrets are mounted on arms on either side of the turret and can ba swung forwards to decrease the overall with so the tank can be stored inside planes like the C-130 or move through buildings without the risk to shear them off.
A load of reinforced MEXAS plates on the top and a reinforced, slightly V-shaped belly round up the Cougar's protection against snipers on rooftops and mines buried in the ground.
In the (hopefully) unlikely case of an NBC attack, the Cougar carries an NBC system similar to the one used in the M113A3 Gavin. Unlike the crew in the M113, the crew in the Cougar does not need to wear a mask, though, as the amount of air filtered only needs to support 3 people instead of 13. The NBC filters also get their air out of a small compartment from where the intake for the diesel engine and the APU are supplied with air. It is connected to the snorkel and serves as a buffer that prevents water and some chemicals to be sucked into the filters and the engine when the tank is submerged or wading through a river.
These protection features are the level of protection of the standard version of the Cougar. Whenever it is forced to fight in a battle where the risk to run into an MBT is higher, it may be equipped with additional armor protection once it leaves the cargo plane. Additional possible armor modules include extra layers of ceramic armor tiles, replacement of the bar armor skirts with ceramic skirts backed up by polyurethane foam in the large gap between the hull and the skirts, additional smoke screen launchers on the turret, and interceptor projectile launchers directed to the sides to fight off incoming penetrators and HEAT shells.

Navigation and Sensors:
Unlike most modern tanks, the Cougar is pretty spare on advanced electronic gadgets. It does not carry any more electronic equipment than a Wiesel Scout vehicle - to be precise, it CARRIES the Wiesel Scout vehicle's equipment. The sensor mast is locate in the front of the turret and can be moved up to 1 meter to take a peek over a wall or when the Cougar takes cover behind the top of a hill, and may scan the area for potential foes. An integrated laser range finder also allows it to spot a target for laser-guided ammunition, which is very practical when the Cougar spotted an enemy MBT. This way, it doesn't expose itself and has no need to test if the IronFist hardkill system works as efficient as IMI pretends. As with the Wiesel scout, the top of the mast can be dismanted and carried to a higher area, which turns the Cougar into a surveillance vehicle. However, this is not the tank's primary function, and should only be used if there is no other scouting vehicle available.
The interior is pretty spartanic when compared to today's "standards". The driver has the basic equipment he needs for driving properly, a waterproof touchscreen monitor provides a map and additional infos from the TC and the gunner, and 5 vision blocks grant him a small view to the world outside. Both the TC and the gunner have the same multifunctional equipment so one can take over if the other one is "unable to". Also, both crew members in the turret have hatches with vision blocks with almost 360 degrees of POV, an additional basic starlight scope like the ones used by infantry (but optionally plugged to a monitor), and a few extra cams to keep the blind spots in view as well. Because of the large turret diameter (1.60 m) they have a lot of room for such a small vehicle - somewhat unlike the driver, who lays in his compartment as if he was driving a Formula 1 car, but with a lot of soft cushions to keep the ride less stressful for him.

Firepower:
A first glance shows that the Cougar did away with the common weapon layout. The main weapon is not mounted in the fron of the turret, but on massive arms on either side. Although this means that the turret and the arms need to be higher than usual to provide the same gun elevasion/depression as other tanks, it also makes the tank notably shorter even with long-barreled main guns, makes fume extractors unnecessary, reduces damage cause by misfires and ammo explosions, and allows that a smaller turret can be used, among with less armor etc. Also, the arms can be moved upwards with two large hydraulic cylinders, which raises the weapons over the turret and allow the cougar to fire while the tank itself is covered, which drastically increases it's survivability.
The Cougar's main weapon are two 57-mm L/55 cannons similar to the russian ZIF-71. Each cannon fires up to 120 57 mm shells per minute, at a muzzle velocity of over 800 m/s. A massive muzzle brake and the double recoil brake reduce the weapons' recoil to a very low level where both the turret's inertia and traversion system can easily chew without knocking the turret out of alignment with every shot. Both cannons are fed by a 20-shot RTU magazine mounted between them, which can be replenished with a second autoloader from the ammo replenisher inside the back of the turret when the guns are moved to zero-level. By default, the main guns fire 57x347SR mm SAPHET (semi-Armor piercing, High explosive, time-fuzed) rounds, which can knock down walls, blow up obstacles like dragon teeth, flatten pillboxes, clear out confined rooms like appartments in cities, flatten light tanks and APCs, and make infantry run away pretty fast when set to time-delay and becoming airburst ammunition (the shells just need to be fired onto the ground in order to bounce back up into the air because of the low angle of impact and detonate a few meters over the ground). Both the RTU magazine and the main replenisher hold up to 80 rounds. Additional rounds can be stored in a small bunker mounted in the aft.
The secondary armament is a 40x57 mm automatic grenate launcher loaded with HEDP shells, which are used when the large shells would be overkill. A single MG-3, 7.62x51 mm, provides backup against infantry. Whenever the situation requires it, the weapon platform can be upgraded with launcher tubes for ATGMs like the MILAN, or recoilless weapon systems like the Panzerfaust 3. This provides limited anti-tank capabilities, but it's not the best solution as there are better units who can knock out an MBT.
If the Cougar encounters a minefield, it can blow a path through it with two mine-clearing harpoons hidden under the large hatches in the front of the skirts. These rocket harpoons fire an explosive cord over the minefiled, whichthen detonates any mines in the tank's path when triggered. The mine-clearing equipment may be swapped with large-bore rocket tubes, which fire a large explosive warhead against an obstacle over a very short distance and blows it up.

Versatility:
With the weapons being mounted outside the turret, they may be replaced with other systems without affecting the turret itself. For example, they can be swapped with a quad-configuration of 30 mm autocannons. The standard sensor in the front can be swapped with a targeting radar, and the standard replenisher can be swapped with a seeking radar. which turns the Cougar into a powerful AA tank. Other equipment like Bulldozer blades, winches, and engineering equipment can be applied to the turret and the glacis as well, as the Cougar is already technically prepared for it - provided the equipment was designed to fit the modular coupling system.

Conclusion:
The Cougar can fight anything up to a light tank, has limited combat engineering capabilities by default, is fully dive-capable and NBC-protected, light enough to be deployed by air, pretty cheap when compared to other tanks, and still provides lots of potential for upgrades. If I had to build a light tank for the 21st century, I'd definitely build something like this.
Thank you for your attention.