[grepex]

It is written in Typescript.

https://github.com/anomalyco/opencode

There is an archived Opencode project written in Go but I don't think it is affiliated.

https://github.com/opencode-ai/opencode

[ValentineC]

This is a pretty good summary of what happened:

https://news.ycombinator.com/item?id=44483251