A Sega Dreamcast emulator called Reicast was added to Google Play yesterday and can be downloaded now for free for Android devices. The emulator though is still in Alpha so expect a few hiccups along the way in terms of “usability, performance and stability.” These have been promised to be fixed in the following weeks.
According to the emulator’s description, you’ll need to have at least a Cortex-A9 dual-core 1GHz+ processor in your Android device to run Reicast properly. You’ll also need the Dreamcast BIOS for the Reicast emulator to work.
Put [the BIOS] on /sdcard/dc/data/dc_boot.bin. The Dreamcast flash should be on /sdcard/dc/data/dc_flash.bin. You should dump these files from your Dreamcast and the games from the original gdroms (gdi or chd format).
On NeoGAF users are already reporting playing Soul Calibur, Sonic Adventure, Resident Evil Code: Veronica and more easily. Reicast also supports Ouya. So in case you have a unit handy, you can opt to play your games on a big screen instead.
You can download the emulator from Google Play.