Sim

Sim is an open-source workspace for building, deploying, and monitoring AI agents. You wire blocks, models, and integrations together on a visual canvas — or just describe the workflow in plain English — and it produces an agent that acts across the tools you already use, from Slack to HubSpot to Notion. The part that stood out to me is the monitoring: you can trace every run block by block, with full logs and the real cost, which most agent tools quietly hide.

It’s worth being honest that this is more team platform than one-person side project — it’s SOC2-compliant and clearly aimed at technical teams. But it’s genuinely open source, so you can self-host and own the whole stack, and for anyone tired of black-box agent builders, that transparency is the draw.