Start here

Three products, three different problems:

If you want to…	Start with
Run an agent session, choose a model, or connect tools	Harness
Give an agent a composable language for computing with host-provided capabilities	Arrival
Model collaborative state with Yjs and MobX	Plexus

You don’t need to install all three to try one. The Harness checkout is self-contained; Arrival can be used as an npm interpreter; Plexus has its own workspace and existing detailed docs. These pages are introductions synthesized from current product repositories, not from the retired wiki or speculative proposals. Follow each page’s source pointers when you need the exact contract.

If this is your first visit, pick a task rather than reading specifications in order: run a Harness session, evaluate an Arrival program, or inspect a Plexus model.