DeSmuME is a Nintendo DS emulator running homebrew demos and commercial games.
DeSmuME can be installed from your Synaptic Package Manager (System->Administration->Synaptic Package Manager) in search field type: desmume and hit Enter. Select DeSmuME and mark for installation then click the Apply button. When installed you can find DeSmuME in your games list (Applications -> Games), as you can see there are now 2 versions installed of DeSmuME (DeSmuME (GTK) and DeSmuME (GTK-Glade) just test them both and use the one you prefer the most….. but on both the emulators the sound is not good (turn it off in config menu) and sometimes the graphics are a bit slow, you can always try to adjust them by changing the configuration by clicking the the Config options.
good luck and have fun 😉