"Steak we followed you for porn not this shit"
TOO BAD, HAVE KNOWLEDGE!

Links:
VTFEdit: http://nemesis.thewavelength.net/in.....php?c=238#p238
GFCScape: http://nemesis.thewavelength.net/index.php?p=25
CrowbarTool: https://steamcommunity.com/groups/CrowbarTool
Valve Dev Wiki: https://developer.valvesoftware.com/wiki/Main_Page

Plugins:
Blender: http://steamreview.org/BlenderSourceTools/
3DS Max: https://knockout.chat/thread/806/1
Maya: https://puppet-master.net/plugins/mesa-2-0/
Cinema 4D R18/R19: https://github.com/xNWP/Cinema-4D-S.....Tools/releases

"Port-ception" section from now defunct sfmnauts site by Taco

DO NOT PORT A PORT.
It may seem tempting to use a preexisting port as the basis for your project. This is a bad idea for many reasons, with the most obvious being that some authors (especially from obscure platforms like MMD/XNALARA) are very protective of their own work and will be quick to go after you and demand credit or removal.

Additionally, keep in mind this is a hobbyist community. The majority of porters are generally inexperienced with 3D concepts, often knowing only enough to port to their platform of choice, breaking all kinds of things in the process.

It's simply bad practice; don't rely on other people to do your work for you. The best way to improve your skills and get better at what you do is to learn how to do things yourself. Apply your own methods and expand on them in future endeavors. Practice makes perfect.

It is incredibly important that you begin your project with a fresh extraction from the game files whenever possible, only utilizing others' work as a last resort for complicated issues where it does not make sense to invest a large amount of time doing something that's already been done by someone else.

Examples of situations where using others' work could be justifiable:

Requiring portions of a mesh to be rebuilt due to import issues
Requiring significantly altered UV maps or texture layouts in order to achieve the correct result when ported
Utilizing necessary texture edits, such as ambient occlusion removal or eye texture conversion
In the case of extensive rigging or bone loss, it is HIGHLY INADVISABLE to rely on others' work to rectify the situation. Poor rigging is by far the biggest common issue shared amongst inexperienced hobbyist users. It's not always the case of course, but more likely than not, you are going to end up importing garbage rigging. Bad rigging is not better than no rigging at all, they are equally unacceptable.

Even if you have no intention of making your own models one day, learn how to properly rig. A model is worthless without a good rig to pose it. Even if your model imports with perfect game accurate rigging, it is highly likely that it won't translate that way to Source or other older engines, due to weighting limitations.

Please see the page on Source Engine rigging for more information on this.

COMMON ISSUES WITH PORTS FROM OTHER PLATFORMS:
Most ports you find for other platforms will be damaged in some way from their original extracted state, unknowingly by the author.

XNA and Gmod users in particular tend to only understand 3D concepts directly relating to porting to their platform, often breaking or ignoring glaring problems in favor of quick results. You are much more likely to find quality work from authors who work with professional game engines such as Unreal or Unity.

XNALARA:

Bone rotations are not supported, animations will never be compatible
Completely renamed bones
Altered skeleton hierarchy
Textures are often modified from their original state, especially specular maps
Damaged mesh data, rigging, and smoothing errors, due to author inexperience
DeviantArt community, so don't expect quality work in general
Garry's Mod:

Bones renamed to Valve Biped format, but usually the old HL2 format
Finger bones reoriented, finger rest positions modified into a claw grip
Double compression on textures, DO NOT extract from a VTF texture with DXT compression
Facial bones are often removed in favor of vertex flexes
Rigging loss due to Source's weighting limitations (SFM is no different!)
Possibly reduced bone count due to Gmod being an older engine branch
Damaged mesh data, rigging, and smoothing errors, due to author inexperience
Semi DeviantArt community, extremely varying levels of quality
MMD (MikuMikuDance):

Skeletons are completely replaced, model is rerigged to a dancing anime girl skeleton
Excessive material reassignment
Textures are often modified from their original state, especially specular maps
DeviantArt/Weaboo community, although surprisingly they often produce much higher quality work than XNA users
KCMM (Brawl Vault):

A place where you may find models nobody else seems to know how to extract, occasionally useful

Skeletons are completely replaced, model is usually rigged to an existing character's skeleton
Meshes are often reduced from their initial polycount to be optimized for the Wii
Downscaled texture sizes
Somewhat experienced community, but also rather whiny, and dead
Gamebanana hosts content for Smash 4, many former users reside there currently
The Models Resource:

Often a good source to acquire unmodified, cleanly extracted models when you don't have the tools you need

Rigging may or may not be included, if it is, it's usually the original unmodified bones and weighting
Original textures and material names are usually maintained
Still subject to any errors caused by the import tools, many users won't fix them before uploading
Usually safe from any additional damage caused by user error, due to very little modification from the base imports
Second Life:

Do not ever use anything from Second Life, under any circumstances

Guaranteed garbage quality and an insane community obsessed with copyright