I was looking into this about a month or so ago so I know of a few.
There is a newer version of Feral Heart called Feral Heart Unleashed (I'm assuming you were referring to the original FH). It is not as active as FH used to be, but it did have a few members online whenever I played it. However, I had some troubles with crashing a couple times.
https://feralheart-unleashed.com/There is one called GLASMAR which I've never played so I can't say if it's actually still active, but seemed to be the main FH alternative as of right now? (But idk the last update on the site is 2020 so now I'm confused lol)
https://glasmar.weebly.com/There is an older IT game I played called Dawn of Eternity which is actually still actively being updated by the owner of the server, and imo has some of the prettiest NPC/enemy models and maps, but sadly hasn't been advertised much and therefore the servers have been dead pretty much every time I've been on it. http://dawn-of-eternity.com/community/
And the only other thing I can think of that is similar but not an IT server, is the EmuFeral/Ferever project, which is basically a fan-run server of the defunct Wildworks game Fer.al. It does have a few players on it, I think a bit more than the Feral Heart Unleashed game. You have to go through their Discord to set up an account and play it though and it can be a bit of a hassle. https://emuferal.ddns.net/index.html
Those are pretty much the only active ones I know of, hopefully I could be some help. ^^
