Most of these source files are derived from decompiled Half-Life 2, Half-Life 2: Episode One, Half-Life 2: Episode Two, Half-Life 2: Deathmatch, or Left 4 Dead 1 content. Crowbar was used to decompile the content involved.
SMDs under `custom` subfolders (i.e. `combine_soldier_anims_anims/custom/Idle1_Pistol.smd`) are custom animations or modifications of decompiled animations created by Blixibon.