Gravity is a module developed inside Transformice, using Lua Script. You can see more information (portuguese) here: https://atelier801.com/topic?f=6&t=859194&p=1
If you want to colaborate with this project, please fork this repository to your local, make your changes in a new feature branch (you can call it 'feat/name-of-your-feature') and submit a pull request. Any kind of PR will be discussed before merge.