The EdisonWatch uses an Intel Edison as the main processor, for Wi-Fi, and Bluetooth. Battery management, 9DoF sensing, display, and input are broken out and/or handled by a single daughter board. The Edison runs Linux so custom drivers and software ties everything together to provide typical, and not so typical, smartwatch functionality.
Sadly this project is ever so slightly dead in the water. The screen used for the project uses SPI (as do many small screens out there) and Edison's SPI support is... lacking. Until Intel can fix so rather large problems with SPI support this project isn't going to be going much further. It's a good thing I know electronics necromancy so when I finally can get back to working on this I can bring it back to life.
Perhaps check these guys out for inspiration/ideas: http://linuxgizmos.com/modular-smartwatch-runs-tizen-on-edison/ & http://www.chooseblocks.com/
They run with an Edison too and were finalists at Intel's Make it Wearable event in 2014.