This is a collection of the community-contributed code for the xAct tensor algebra package for Mathematica, which can be downloaded here. The best place to go for questions is the xAct mailing list. You can find our repositories at @xAct-contrib on github. If you have contributions, feel free to send pull requests.
If you've never built a Mathematica package before, this might seem a little daunting. That's why we've provided a “Hello World” template/example package named HelloWorldxTension. This example covers the overhead of dependencies, scope, etc. and shows how to use xTension to add a message to print from DefTensor.