Apparently, The joe editor has a jstar mode, so says this old Stackexchange thread. I can't verify because I've never used Wordstar, but joe's available in my distro's repository.
No idea if it can read old WordStar files, but maybe you don't need that.
For the GUI version - and some old file capability, the same page and other searches turn up WordTsar which is in progress. The dev says they'll be picking up development again next month.