Buildcraft contains many different things but doesn't reach its limits.
That is where the many addons / compatible / complementary mods come in.
Addons can be anything from making a pipe on the side of a block place items in the top slot to making completely new machines.
This wiki does not provide support for any of the mods/addons shown below.
Please refrain from asking questions relating to non-Buildcraft mods.
Have you ever wished CACACACCACACACACACCACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACACAC and rails had received a bit more attention during Minecraft's development? Well that ends now! Gone are all those broken bits and in their place are a ton of new tools to build your massive rail system. If you ever cared about rails, you wont ever look back! This mod also includes a whole new fluid: Steam! Steam is used in RailCraft's engines to make Minecraft Joules from BuildCraft. Many of RailCraft's machines require Minecraft Joules to operate. Wether you want more power options or amazing new minecart rails, having BuildCraft installed along with RailCraft is a great idea!
Forestry allows fully automated farms such as tree, wheat, and netherwart farms, to be built and run easily. Forestry originally had BuildCraft as a prerequisite so you know having BuildCraft installed with Forestry is a great idea. Forestry includes new engines, powered by items that are only available through farming in Forestry to gain masses of power. All the farms in Forestry are run on Minecraft Joules so if you want to farm successfully, BuildCraft and Forestry work brilliantly along with each other. If you want to automate your farms, you can do so very easily with BuildCraft pipes and a few extra pipes added by Forestry to help automate the production of Bees, Trees and Butterflies! (Yes, Forestry includes bees, trees and butterflies!) Forestry has been designed with compatibility with Buildcraft and Industrial Craft in mind. Forestry is developed by SirSengir, one of the current authors of Buildcraft.
IndustrialCraft is a mod featuring many new machines such as Macerators for doubling ores (which can be very useful when creating more complex items such as Quarrys) and Electric Furnaces. Pipes in BuildCraft can be a pain in the backside to craft, especially when running low on glass. IndustrialCraft gives the player the ability to grind cobblestone into sand to then smelt into glass. Pipes made easy! Buildcraft is highly recomended to pipe items to/from IndustrialCraft machines to create some rather impressive automated factories.
Thermal Expansion is a great mod and is expanding rapidly. It uses BuildCraft's API to add a pair of engines, using a couple of differes to make eneedstone Enginee game and each liquid has a different, unique effect. This mod really needs to be seen to be believed.
MineFactory Reloaded adds tonnes of new machines that allows for lots of new, different ways of automation and new things to automate from easy farming to turning mobs into liquid meat. Yes. I did just say liquid meat. MineFactory Reloaded adds a hand full of liquids from liquid meat to sewage to pure essence of mobs. All of this is only creatable with BuildCraft's API! All of the machines rely on BuildCraft's power to function .
Sneaky Pipes (not updated)Edit
Sneaky Pipes adds the functionality of the previously mentioned side block top slot mechanic allowing for some easier piping systems.
Additional Buildcraft Objects adds many new pipes for BuildCraft including liquid and power valves, diamond liquid pipes, and tank liquid balancing pipes, among others.
Buildcraft Tools adds a bunch of chargeable Tools and Armor to Buildcraft.