I have been spending my leasure time with CooCox library. They provide CoIDE, CoFlash and Cox library. CoIDE is simple and fast to set up, possible to use J-link, OpenSDA and many more. I was worried in the beginning because of eclipse and some experience with other IDE which I was not fond of :) It turned out great, eventhough it is still under development.
The source code is on GitHub and forum is alive.
CooCox supports Cortex M0 and Cortex M3 so far. Next step is to try their CoOS, but that has to wait a bit. Still many areas to explore in their interface.
CooCox website [coocox.org]