Fiction River is a series of anthologies from WMG Publishing. The first one published was Unnatural Worlds, back in 2013. I recently read it after picking it up in a Storybundle.
I was pretty sure going in that many of the twelve stories would be solid since I recognized the authors. And this was in fact the case, with names such as Esther Friesner and David Farland, plus stories by each of the editors. I'd not encountered most of the other authors before, but given the experience of the editors, I wasn't surprised to find that I enjoyed most of their stories as well.
While the theme of the anthology is stories that deal with different worlds, the stories treat that theme very differently. Some are literal, such as Devon Monk's Life Between Dreams, where the characters actually walk across multiple worlds. Others are more symbolic, dealing with characters that come from different worlds, such as Ray Vukcevich's Finally Family.
My personal favorite is Esther Friesner's The Grasshopper and My Aunts, which was fairly predictable since I've read a bunch of her books. It's written in Victorian-era style and deals with Greek myths living in the English countryside. Quick moving and humorous throughout.
I like the idea of the Fiction River anthology series, and there's plenty more of them by now. Unnatural Worlds is a good opening effort. I'll probably seek out some more of them in the future.