Jules is the first and only one to add a full API, which I've found very beneficial. It lets you integrate agentic coding features into web apps quite nicely. (In theory you could always hack your own thing together with Claude Code or Codex to achieve a similar effect but a cloud agent with an API saves a lot of effort.)

Google ADK is real nice and gives you an API as well (also web browser and terminal prompt)

Jules is nifty. Weirdly heavy on the browser CPU.