I didn't like any of the "agent development environments" I found out there as none had all four of: 1. Nice, human-readable interface: Like Claude and ChatGPT websites - simple to read, without monospace font, annoying terminal edit behavior, and messy tool calls cluttering the information. 2. Supports work on multiple machines: one client can reach agents on multiple machines, so agents can keep chugging even if I close my laptop. 3. Separate worktrees per agent: so agents don't clash while they work. 4. Cross-model: So I can run Claude, Codex, Hermes, etc on the same projects. So two days ago, with @claudeai Fable 5, I started building. Today, I've been using the product all day. I'm calling it Leather, because like the material, it is meant to be simple, versatile, and beautiful.