Indiket of dreamcast.es released Allegro DartsDC, a port of Allegro Darts for the PC. This games is based on the popular Allegro library, a development library that facilates game development a lot. Chui and other members of dreamcast.es are currently porting this library to the Dreamcast. Allegro for Dreamcast is not yet publically available.
Although you can play with the pad, this game should be played using the mouse (although mouse support hasn’t been tested yet). You can open the menu by pressing X or Y.
Source:SEGA-DC.DE and Dreamcast.es