contiki-launchpad

While it can't use an external xtal, it still has an internal crystal oscillator which can clock it at some MHz, up 16 MHz I think. It's not as accurate but cheaper and more flexible. I did a port of the Contiki OS to the Launchpad, which now comes with the msp430g2452 (16kB flash/256 B RAM) and the 'g2553 (16/512). At home I have them using cc2500-radios (2$ modules from aliexpress) and a radio duty cycling protocol I wrote, with plenty of flash space left for user applications. You can find the port at https://github.com/msloth/contiki-launchpad and a write-up at http://www.bithappens.se/blog/2013/05/26/contiki-for-ti-msp4... and http://www.bithappens.se/blog/2013/05/26/simple-yet-efficien... with lots of measurements and other crowd pleasers.