[Burrytar]

Of mushes and muxes that I've played, the one most like Crossroads is probably Firan Mux. Paragraph-length poses. Medieval + classical themes, etc. There are a few major differences. Firan has a roster system, so you wouldn't make your own character but rather pick one that was predesigned for the story. Firan is objectively far more active than Crossroads ever was. It's treatment of magic is more subtle and more divine than individualistic in nature. And it's theme is less egalitarian and sometimes quite gritty for the purposes of allowing opportunities for conflict.

If you don't mind a different theme altogether, you might try The Reach Mux, another very active paragraph-rp game. It is modern-world World of Darkness and very flexible as far as character creation goes. The main drawback is that you'll want to invest in at least one WoD rulebook. It also has more of a focus on mechanics than either Crossroads or Firan.

If you enjoyed the show Firefly, you might also give Serenity Mush a go. Or for that matter, Otherspace. Being scifi, the themes of themes of these games are the least like Crossroads, however, but the playerbase and styles aren't so different, I'd say.