DeSmuME is the most seasoned open source Nintendo DS emulator. It sports tools designed for hackers, speedrunners, youtubers, and casual gamers. Homebrew programs are supported and can even be debugged through GDB.
The Windows and OSX versions are both relatively feature rich, and there is a small universe of forks and mods that add even more features for casual gaming.
DeSmuME is the origin of RetroArch and OpenEmu Nintendo DS support and is used by several mobile Nintendo DS emulators, with the notable exception of DraStic.
DeSmuME's source code is now hosted at https://github.com/TASVideos/desmume/
Auto
Find your games and select the cheats you want, then click on Send cheats to plugin.
Manual
Go to File > User database... or pressing F3. Press Add Cheat to add new database. At the right side, you way write down your database title and the cheat codes. Tick your database and press OK after done created. Click on Send cheats to plugin.
A PSP emulator for Android, Windows, Mac and Linux, written in C++. Want to contribute? Join us on Discord at https://discord.gg/5NJB6dD or just send pull requests / issues. For discussion use the forums at forums.ppsspp.org.