For my game development work, I primarily use 3D Studio Max. I don't necessarily think it's better than Blender or Maya, but it's the tool I feel the most proficient. Additionally, I like animating with its built-in biped. It's not perfect, but has a lot of useful tools, and it's much faster for me to setup than trying to rig a character from scratch.
However, I've always wanted to make a biped that could control a humanoid rig without affecting the original rig. That is where this maxscript, which I call Biped Constraint, comes in. With that, I can create a biped, size it to match my humanoid character, align it to my humanoid rig, and ultimately use it to drive my humanoid rig's animation, which then can export cleanly to a game engine such as Unity3D.
Though this is a very obscure use, I have found that others have found it useful, so I've made this maxscript available for purchase on my itch.io page. If you would like help with this process, or just prefer to not do it yourself, you can hire me through fiverr as well. I also have a gig for converting .fbx animations to biped animations using the same tool.