JPCSP is an emulator for the Sony Playstation Portable. It is the first emulator for the PSP made in JAVA, which is no small accomplishment. This makes it possible for JPCSP to work on all the platforms that support Java. I don't think the Mac would have a PSP emulator if it wasn't for JPCSP.
JPCSP can run both commercial and homebrew games. The support for commercial games is limited and most games won't play well. Fortunately, the dedicated users of this application have created a compatibility list that shows which games work fully, partially or don't work at all.
You can load games from their UMD disks, memory sticks, or even image files. The emulator has support for snapshots, which is basically another word for gamesaves. You can create a snapshot while you are playing and when you load it the game will continue from exactly the same spot where you saved it. All of the application configuration options can be accessed either via the menus on the menu bar or from the configuration utility.
In my testing, I played one of the games that was marked as playable on the compatibility list. The game ran just fine and I was able to play it without problems. The emulation speed was pretty good as well.