It's all very regular: MySQL, PHP on Yii 1.1 (want it bad to upgrade but have no time right now), Apache, nginx as proxy, some light AWS services usage, Redis for cache. I think that's it on the server side. On the client it's custom-coded jQuery based UI. TypeScript and LESS are used for it. The rest is how it's made: everything time consuming is processed in background, UI inteacts with backend via async calls. API is used by mobile apps as well.