Came across this and didn't see it mentioned previously on 43oh or Stellarisiti. This company has made their commercial RTOS available for free for selected "maker" platforms from Freescale, ST and TI. The primary board of interest for the TI camp would be the TIVA TM4C123 Launchpad (they also offer it for the TI DK-TM4C129X, not the TM4C1294 Launchpad). Appears to be compatible with IAR only however. Short blurb from the offering page:
"smx Learning Kits (L-Kits) are free, fully functional releases of the smx kernel for non-commercial use in personal and class projects, proofs of concept, and prototypes. They are available for several low-cost boards that are popular in the DIY / Maker community. L-Kits utilize the powerful EWARM development suite from IAR. (A free size-limited version is available; see below.)
L-Kits are offered as a community service to allow people to learn how a full-featured RTOS operates and to experiment with using it. They are also intended to allow doing class and other non-commercial projects requiring an RTOS. There is no time limit, and users will not be contacted by a salesperson."
http://www.smxrtos.com/lk/#lkcont
FWIW....
EDIT: Looked at the ad again and noticed that they had the TM4C1294 Launchpad pictured among the boards in the ad... even though it isn't listed as a supported board. It would be cool if it actually worked on that board utilizing their ethernet stack.