User's guide & Installation guide for the current GATE release can be foundhere.
We warmly recommend to use the latest GATE release when available.
For the next release (GATE 10), already available in beta, user and installation guide can be found here.
Documentation with ReadTheDocs
User documentation frequently evolves so members of the OpenGATE collaboration have set up ReadTheDocs toolkit to help them work more efficiently with such a dynamic content. You can easily propose modification in any page of the documentation by using the 'edit on GitHub' button from the small menu in the bottom right corner of the page ('v:latest'). It will open an editor to make modification that may be then submitted by using a Pull Request. Once reviewed and validated by the Gate dev team, the modification will be available for everyone.