XRoar is a Dragon emulator for Linux, Unix, Mac OS X, GP32, Nintendo DS and Windows. Due to hardware similarities, XRoar also emulates the Tandy Colour Computer (CoCo) models 1 & 2. Get it here --> http://www.6809.org.uk/dragon/xroar.shtml
The download page is here --> http://mamedev.emulab.it/clrmamepro/download.htm but note the actual download links are wrong on the page, but i'm sure you can work them out.