pewMaster is a free-to-use (fair-use) masterserver that can be accessed via HTTP.
That way it is usable by almost any language/framework. It keeps a list of open sessions (until they get closed or time-out) that can be queried by game/app.
pewMaster does NOT do NAT-punchthrough. It's just for listing sessions and exchanging ip-addresses.
The API is quite simple (CRUD).
The sessionhost has to create a session to get an sessionid.
Afterwards the sessionhost has to update the session, otherwise the session will get dropped after 5 minutes. When the session is closed by the sessionhost it can close the session to keep the listing clean.
The client can only list the sessions. (max. 1000 results)
Got further questions, problems or just wanna say hi?
Feedback and suggestions are welcome as well.