Yep along with Spigot, as mentioned by _jomo, there's also a new project called Sponge that is replacing CraftBukkit from the ground up, building on top of Mine

Yep along with Spigot, as mentioned by _jomo, there's also a new project called Sponge that is replacing CraftBukkit from the ground up, building on top of Minecraft Forge (a modloader) rather then as a standalone mod like CraftBukkit/Spigot. Its still in pre-alpha though, and there are a LOT of things unimplemented, compared to Spigot which is a fork of Bukkit. Another popular option is Glowstone, which is an open source implementation of the entire minecraft server, rather then a mod. Glowstone already supports plugins written for the Bukkit API (separate from the CraftBukkit implementation that got DMCA'd) and there are plans to support the Sponge API when its more mature. I can't speak to its stability/completeness though. It looks like there isn't any redstone or physics yet? That shouldn't be a huge deal for most creative servers, but YMMV.