Emby Party is a solution for watching videos with multiple friends through your Emby web client. It requires no additional dependencies - only a device running Emby (presumably with good enough hardware for all the attendees, especially if you're transcoding) and at least one web browser.
It consists in two halves: A server plugin and a web client module. They must be used together! Each half expects the other to be present.
This is an experimental open source project. Feel free to fork and contribute pull requests and issues (my availability for fixing issues on my own may vary wildly and may be low in the near future). The source code and all known issues can be found here.
Currently testing in Emby 4.8.10, Windows and Debian Bookworm (Linux), Firefox, Chrome and Edge.
Readme coming soon!