While there is no official version of Garry's Mod (GMod) for the PlayStation Portable (PSP), you can create a "better" GMod-style experience on the handheld by utilizing the homebrew community's creative ports and sandbox-style mods. 1. The Closest Alternative: "GMod PSP" Homebrew
GMod requires dozens of keys (Physgun, Toolgun, Context menu). The PSP has 12 buttons. This is the #1 complaint stopping gmod psp better from feeling intuitive.
Conclusion
The Quest for a Better Gaming Experience: Why Gmod PSP is the Ultimate Choice
: While restricted, the level creator in LBP is the closest "official" sandbox experience on the console, allowing for complex physics-based contraptions. Pro-tip: For the most authentic experience, look for NZP (Nazi Zombies Portable)
"How are you so good on this thing?" one of his friends asked.
It is important to be wary of certain content claiming to be "GMod for PSP": What will happened when Garry's Mod Ported to PSP? Thread