I have a LPC2138 (32k ram and 512 flash) based development board. Latest time I started work of porting ucOS 2 toward my development board. Although I have made some bad assumptions what result in rather not fully functional RTOS, and a poor performance, I realized great potential of running system on top of RTOS. Now I am going to port something more complex I think ecos is very powerful and decent rtos. But I am worried if I have enough memory to accommodate so complex thing. I know that there is possibility to configure ecos maybe if I get rid of most of feature I will be able to use this. Please share your opinion on topic. If ecos is not suitable please propose me other open source RTOS but something different than ucOS 2 because I want to study more on this topic. (After all ucOS is not free of charge)
FreeRTOS?
also, consider DIY cooperative scheduler for multiple finite state machines
Nobody can share experience about ecos 
So probably I have to analyse the problem on my own. If I achieve any results I will share with you my experience in this topic.
I agree that FreeRTOS is something what I should be familiar with. Whatever I will fail with ecos or not I also analyse potential of this rtos at some point in the future.
After some investigation I find FreeRTOS is well suited for my needs. So if I will write something in future using arm7tdmi based processor I probably would use this environment. It is easy to deploy and easy to use.
To investigate more about operating systems I turn toward linux and my PC as test environment. When I learn what is going on I probably would try ecos with my pc as well.