I built one using GPT-4[1]. It's not perfect but is working quite well and is now being used by hundreds of users, apart from me, to work on real, non-toy tasks. For example, I used it to build most of a production-ready AWS infrastructure (and accompanying deploy script) with the AWS CDK.

I want to add Mistral support soon, probably via together.ai or a similar service.

1 - https://github.com/plandex-ai/plandex