The original Droid800 emulator is based on the classic Atari800 emulator Source code for Droid800 doesn't seem to be available anymore. The last reference can be found on the AtariAge forums:
http://atariage.com/forums/topic/192841-droid800-emulator-for-android/
To build it you need the SDL port for Android that this emulator depends on, and the RetroX libraries
https://github.com/fcatrin/rbxAtari800AddOn
https://github.com/fcatrin/retroxlibs
This port is used by the RetroX frontend http://retrox.tv