Our stack is:
Backend:* object-oriented PHP, Composer/PSR-4, PSR-2, Eloquent, various third-party components, PSR-7
Frontend:* JavaScript (ES6), Mithril.js, gulp, babel, npm, bower, LESS
Not all of them will be essential to know in order to contribute — it depends what you're doing 🙂 We'll be working on some extension development docs for beta.
