Multicam
For easily creating general-purpose overlays with cam-sharing, images, texts, videos, and other stuff, that possibly multiple streamers want to include in their stream, a tool called "Multicam" has been developed and hosted as multicam.moetz.dev. Rooms cna be created, and then in a room, different items can be added and arranged.
To be honest, the UI and UX for arranging a room / items in it needs a lot ot improvement to be actually easily usable, but once configured, it does its job well.
For this tool, I also for the first time made sure, it's available in multiple languages.
And, it's open source here!