DeSmuME is a Nintendo DS emulator developed by YopYop156 for Mac, Windows and Linux. He has stopped working on it in the beginning of April 2006 and passed the torch to Yabause team of developers.
melonDS is a work-in-progress Nintendo DS emulator aiming for better performance than DeSmuME and to emulate Wi-Fi and local multiplayer capabilities. It's developed by Arisotura (formerly know as StapleButter), a former contributor to DeSmuME.
NO$GBA (pronounced "no cash GBA") is a Nintendo DS and Game Boy Advance emulator for Windows & DOS. It is one of the first Nintendo DS emulators to successfully run games, as well as being the only known DS emulator for DOS. NO$GBA was developed by Martin Korth.