He has his own emacs clone named QEmacs[1] which I think he uses personally. He uses Subversion as his version control system (at least in developing QuickJS) according to this post[2] by him in quickjs-devel mailing list.
Linus has his own port of the venerable MicroEmacs[1]. As does Walter Bright[2], by the way.
qemacs is actually quite advanced, and even includes a basic HTML renderer (for the help). I was half joking that with quickjs, one now can make a reasonably modern web browser out of bellard-ware…
[1]: https://bellard.org/qemacs/
[2]: https://www.freelists.org/post/quickjs-devel/Please-consider...