EasyRPG claims to be a free, open source alternative that's even compatible with RPG Maker 2000 & 2003. Havn't used it, so don't know how well it succeeds as such.
Wolf. What RPGmaker should be. I don't know about ports.
Wolf doesn't have a saturation channel on recolor commands though, that's rather annoying.
I would just recommend pirating rpg maker, seeing as you weren't planning on buying it anyway.