ZXDS is an upcoming emulator of Sinclair ZX Spectrum for Nintendo DS, written by Patrik Rak. It is still in a very early stage of development, but it already has some noteworthy features, like emulation of Spectrum 128k (including sound) or TAP/TZX/PZX support.

There are two versions, ZXDS.nds for Slot-1 (DS slot) based cards, and ZXDS.ds.gba for Slot-2 (GBA slot) based cards. Just choose the one which suits your card best.

Thanks to http://www.dcemu.co.uk for the news.