Garry's Mod (GMod) is built on the Source engine, it cannot run natively on a PSP
No active development since 2014.
: A massive collection of character models, including beta characters and unique edits. gmod psp
Much of the PSP's most impressive homebrew, like Nazi Zombies Portable or Kurok , is built on modified Quake engines . Some hobbyists have attempted to build "GMod-lite" experiences using these engines, though they rarely reach a finished state. Garry's Mod (GMod) is built on the Source