master & servant webapp thingy first feature should be creating a "session" and "joining" it - the session being essentially a WebSocket connection.
to-be-master sends a request to start a session, stating e-mail addresses to invite as slaves.
The server creates a session, with the initiator being the "master". Invitation emails include links to join as slaves.
Stuff to do:
- web page for session creation
- REST API that it calls
- email sending for the invites and
- web page for displaying a session
- a skeletal WS connection handling joining the session and informing the master of joinees. there should be an API for joining, of course.
Each "session" or "room" or whatever would have a unique identifier assigned to it, so that the web part can support multiple concurrent sessions. Back-end could at first just hold everything in-memory, since sessions won't survive reboots or crashes anyway. And there wouldn't be much to hold: basically a data structure storing the sessions, and the users and their roles.
Angular on the front and Java+Vert.x in the back? Optional Vue or React and Kotlin+Vert.x