Basically OHR is a game making engine that specializes in RPG games, much like RPG Maker, except that it's free and open-source. The only issues it has would be that you need separate programs to make sound and battle backgrounds. (I have no idea what RPG Maker's limitations are with the newest version) It can be found here:

http://rpg.hamsterrepublic.com/ohrrpgce/Downloads

Has anyone here ever used it before, and if so, what do you think of it?

I think that I'm so tired of jRPG-like visuals that I just skip all the games using it, really. OHR can't go into direct competition with RPG maker - if it wants to succeed, it would have to do its own thing. As it stands, we will just get loads more jRPG-like games out of another software for creating them and they won't even manage to get my attention (and yes, I do realize that those games are by far the easiest to make. That's why I believe that such utility for a completely different style would be handy - nowadays, it's really not that difficult to just code your own jRPG engine. Any other tho...) On the other hand, perhaps they do support different styles - I'm just judging based on products.

There are actually quite a few open source RPG toolkits/engines, according to http://en.wikipedia.org/wiki/RPG_creation_software