The stuff on JSR is lifted out of Deno. JSR can install packages for Node and Bun [0]. Most of the "@std" packages in the link above claim support for Bun (the right hand of the package list "stack of avatars" will have the Bun avatar; easier to read on individual package pages where it becomes a header, though), and there is a Bun test matrix in the GitHub Actions CI. (Right now it looks like it just has Bun latest in the matrix, though.)

In terms of coordination, I don't see any obvious Bun contributors in a quick skim [1], but it seems open to contribution and is MIT licensed.

[0] https://jsr.io/docs/using-packages#adding-a-package

[1] https://github.com/denoland/std/graphs/contributors