SFM is a tool published by Valve Software for 3D animation and moviemaking using their inhouse Source engine. For the last several years fans have been putting out tons of videos, dramatic, artistic, comedic, experimental, whatever.
One relatively common topic for animation made for web (3D or 2D) is for visually depicting funny moments of dialogue from podcasts, webisodes, or Let’s Plays–whenever multiple people are talking to each other but there’s no footage of them in person.
For example: the Best Friends, a group of Let’s Players who upload to YouTube, commentating while one of them is playing the game Dark Souls 3:
I love this stuff.