TIL #hy is not the only lisp-on-python, there's also #hissp.
Hy is older (first commit in 2012), has the larger community (hosted on the hylang org on github, not an individual account) and releases more frequently (latest pypi 3 months ago).
Hissp had its first commit in 2019, is hosted on an individual github account, and last released to pypi two years ago. On the other hand the repo is lively, had its latest commit 3 months ago, and that commit was not by the repo owner.
They are difficult to compare in a brief statement, but calling hissp more experimental seems fair.
I'm working off osmosis and first impressions here, so feel very free to correct me, but it seems to me that Hy is happy with providing a clojurish syntax and a defmacro around the Python AST, whereas Hissp feels more like a different and exotic language that compiles to the Python AST.