Windows launcher
SteamRelay.
A Windows relay for bringing local games and applications into a shared Remote Play session when they were never designed to arrive there themselves.
Remote Play Together is great when a game already understands it. The interesting gap is everything just outside that: local multiplayer without native support, useful tools, small shared experiences that would work if they could just cross the boundary.
SteamRelay uses a compatible Steam game as a relay. Steam handles the invite and control layer; the relay opens whatever the group actually wanted to share.