RetroAchievements are similar to XBox achievements or PlayStation trophies, except that they're created and defined by a volunteer community. Just like other retro consoles, the PSP itself has no native concept of achievement/trophies. However, this can be added with emulation!
Not only achievements are supported, but also global leaderboards in games that have scores or times.
RetroAchievements are supported from PPSSPP version 1.16. The feature is not supported in 1.15.4 and older.
From 1.16.1, you can find RetroAchievements under Tools in settings, previously it was under System.
First, create an account on the RetroAchievements website. Then, in PPSSPP's RetroAchievements settings, enter the same username and password.
After that, simply run games, and if they have achievement sets made for them, they'll be activated. Also, you might want to enable Hardcore Mode, see below.
In Hardcore Mode, a number of the emulator's features that are particularly prone to cheating are disabled, such as save states and slowing down time. Speeding up time is still allowed.
NOTE: Leaderboards are only available in Hardcore mode.
We previously called it Challenge Mode, but we have now switched to the RetroAchievements standard, which is Hardcore mode.
Lets you unlock achievements again. Note that this does not affect the real unlock status - you'll just get the notification again if you fulfill the conditions, such as completing a level or whatever it was. This is mainly useful for development - for regular gameplay, it gets confusing.
These are achievements that have been removed, or are in development, or have simply been considered not really worth having.
Usually, turning on this option is not very useful - if you need it, you know you need it.
Find the list of PSP games with achievement support here.
Unfortunately, it's often the case that only one or two regions of a game are supported. Click the link "Supported game files" on the game's page on that site to find out.
Turn on hardcore mode.
All existing achievements were created for the PPSSPP core in RALibRetro, which has the same timing and plugins as RetroArch. Unfortunately, due to deficiencies in libretro's design, achievement checks don't run at the correct time in RALibRetro or RetroArch - so if your achievement works correctly in RetroArch and not in PPSSPP standalone, the achievement is broken.
Achievements are best developed with emulators supporting something called RAIntegration. PPSSPP does not yet do that, unfortunately, so your best bet is still RALibRetro. RAIntegration support will be added to PPSSPP in the future, but I can't give a time frame - things are in flux with regards to RAIntegration vs rcheevos, and I don't want to implement a solution that will become outdated.
Simply go to the RetroAchievements website and sign up for an account. You can then sign into that account in PPSSPP.