Ballistica is the engine and infrastructure behind BombSquad (and maybe more fun stuff in the future). A number of its components are open source, and it encourages modding, tinkering, and community involvement. Check out the links below to learn more.
This site works with Ballistica accounts (also called BombSquad 'V2' accounts). These accounts are replacing legacy 'V1' BombSquad accounts starting in BombSquad 1.7, and they add support for new and upcoming features such as cloud-based modding and the squads system.
The easiest way to get a Ballistica account is to open BombSquad and sign in using Google Play Games or Game Center. This will automatically set up an account for you. You can also create an account here using an email and password.