Supabase is an open source Firebase alternative. Start your project with a Postgres database, Authentication, instant APIs, Edge Functions, Realtime subscriptions, and Storage.

Supabase

Does anyone know what web server the hosted version uses?

x-powered-by says "Express", so probably Express?

I was figuring out if the self hosted version provided variables for supporting HTTPS directly

Instead of using nginx as a reverse proxy for the studio part

I would just use whatever's available for you - having a reverse proxy is surprisingly handy in the long run (you can delegate some URLs to other services, add logging, add anti-(D)DoS etc.).