I roll my own on Node.js. Each agent is an Express endpoint running in a V8 isolate — they communicate through a shared MongoDB layer where each agent reads/writes its state. Data passing is just JSON documents with a pipeline ID linking them. For orchestration I use a simple coordinator endpoint that chains the agents sequentially or fans out in parallel depending on the task.

Observability is the part most people underestimate. I log every agent run with input, output, token usage, and latency to a dedicated collection. Simple but it catches failures fast.