Xronos Board is brains of the Xronos Clock.  It is kind of a Arduino clone but with lots of extras.  You can use it on many of project not related to Xronos Clock.
While board doesn’t support standard Arduino shields, it can do much more than regular Arduino! It has built in Real Time Clock w/ battery backup, microSD card reader, RFM12B radio tranciever and audio processor capable of playing back uncompressed WAV files (mono 22Khz) of any size. And with minor tweaks it’s compatible with many Arduino libraries (some of them were already modified and available on this site for download)  and easily works with Arduino IDE.
16 pin IDC header has 7 data pins (plus VCC and GND) connected to microprocessor and will work with at least two 16×32 Sure’s bi-color LED matrix displays and four 16×24 Sure’s LED displays!  Or use them for your own hardware.
Button header (already complete with pull-up resistors) supports 3 buttons.
Temperature sensor header supports DS18B20 temperature IC .
And there are more headers available for your own custom connections!