Homebrew exists for many systems and platforms, including the PSP. The PSP homebrew community has been very active in finding ways to get homebrew software to work on all PSP firmware versions (only the latest versions are incapable on running homebrew at all), despite Sony's continuing attempts to stop them.
It has been pointed out that many PSP users want homebrew in order to be able to run pirated games, but many others simply want to add functionality to their machines and do cool stuff no possible with the official firmware releases.

