First of all thank you for a good web service.
I want to know is there any limitation for building open source apps? For example if I want to compile something like gcc and ran it’s tests.
Thanks in advance.
there are none to my knowledge. you can do just about anything but host sites for the public.
You can use the web IDE for creating open source projects, there are no limitations. You can designate your project/workspace as an ‘Open Source Project’ and make your project available under the terms of an open source license.
Also have a look at the C9 terms of service: https://c9.io/site/terms-of-service, especially paragraphs 4.3. and 7.1.