I see now there is quite a lot out there now for managing agents to write software, but
a) I started working on this before a lot of them, and b) there are things in Puppet Master that just don't exist all in one product.
For me I'd say the highlights are:
1) Web instead of terminal -- it's just a richer interface
2) iOS app so I can keep working on things from anywhere
3) Local + Remote workers (heterogeneous fleet), I work on things that are cross-platform and PM lets agents spawn across the fleet depending on workload needs.
4) Connections - first-class support for integrating MCP and REST API (ala OpenAPI definitions) into your agents. This goes above and beyond what a single harness can do via i.e an MCP integration. PM imports it (scoped to a bucket/project) and associates it to a policy. It lives between the agent and the remote MCP/API and enforces a policy. My normal flow is give full read access to agents and any APIs that do writes, approval needed. PM has native approval UI on web AND mobile so you can give real agency to your agents without being too permissive.
5) Code review interface is nice, 1-1 discussions on comment threads in the review, pretty responsive.
6) Forwards/artifacts allow agents to share static artifacts/html/etc,. OR serve up any dev server. This is proxied so even things on remote workers "just work" and you can access them, securely.