A remote desktop you host on your own Windows box and use from your iPad, Mac, or Linux machine. The streaming pipeline is inherited from the game-streaming lineage and it is genuinely good. Everything that assumed you were here to play a game got thrown out.
Vessel is a fork of Apollo, which forked Sunshine, which forked NVIDIA's GameStream, a thing NVIDIA killed because too many people liked it. That lineage produced a low-latency streaming pipeline that is hard to beat, and it is the part worth keeping.
The part not worth keeping is every assumption underneath it: that the client is a controller, that audio is one-directional, that a stylus is a novelty, and that latency only matters when something is shooting at you. Vessel rebuilds those assumptions around a person trying to get work done on a tablet.
Vessel is an internal Locke Werks product and the source is private. It is a GPLv3 fork of Apollo and Sunshine, and it inherits their licensing obligations.
For access, licensing, or a conversation about the setup, write to archon@lockewerks.com.