PEG.js is currently maintained by Futago-za Ryuu. Since it's inception in 2010, PEG.js was maintained by David Majda (@dmajda), until May 2017.
The Bower package is maintained by Michel Krämer (@michelkraemer).
You are welcome to contribute code. Unless your contribution is really trivial you should get in touch with me first — this can prevent wasted effort on both sides. You can send code both as a patch or a GitHub pull request.
Note that PEG.js is still very much work in progress. There are no compatibility guarantees until version 1.0.