Minecraft Feed The Beast, FTB servers
Feed the Beast or FTB servers are running Minecraft FTB modpack which would implement various mods such as FTB IndustrialCraft, FTB BuildCraft and many others.
Feed the Beast client?
Since FTB is extensive modpack that adds many feature, you will need custom Minecraft launcher in order to join Feed the Beast servers, the client is free but you won't be able to join FTB servers without it.
Popular FTB mods
Feed the beast has more than 50 server mods, one of the most popular being Direwolf20's modpack. FTB mods add multiple tools and new features that enhance players experience and automate boring tasks.
Feed The Beast is a group of server and client developers that specialise in making high quality modpacks and maps for Minecraft servers. FTB started out as a custom challenge map in Minecraft server that made heavy use of multiple FTB mods.