From the creator's website :
"How would you like to be able to run compiled programs from a uSD drive? Maybe you'd like to create an app that's closed source? Or perhaps you're just looking to display full screen 320x240 bitmaps using the Arduino. If any of those sounds like what you're looking for than Pyxis is the OS for you.
Composed of 1 core and 5 libraries, Pyxis OS is brimming with capabilities and features. 100% free and open source Pyxis is yours to do with as you please. After nearly a year in development we're proud to present this OS; with it you can put a 8.3 file system on your EEPROM, easily work with LCDs, and of course access a uSD drive with ease.
Each of the primary pieces of the OS has their own library. PyxisSD for uSD access, PyxisFAT for the EEPROM file system, PyxisPad for interfacing with the ButtonPad, PyxisLCD for communicating with the LCD and Pyxis for the top-level management of all the pieces."
Another addition to my to-port-list to the mighty PSoC 3