Minecraft forge is the mod that you will really need because Minecraft Forge will allow other mods to work on your client and work correctly. For example, BuildCraft and RedPower mods will need minecraft forge to work.
Minecraft forge is an minecraft API which provides extra modding capabilities. These capabilities have been added to provide support for the different mods using the Forge. You only need to do this once for all mods requiring it. Note that certain mod may include Minecraft Forge in their code, in which case you don’t have to install the forge, but it’s no harm to add it on top of the existing installation.
Minecraft Forge API Features:
- Infinite terrain and sprite indexes
- Support two-pass rendering
- Custom redstone connection direction
- Override block replacement/deletion
- Secondary properties for block (isNormal, isReplaceable, isAir, isBurning)
- Allow an item to have the first callback on a mouse click
- Custom explosion resistances by block and direction
- Custom filled buckets
- Custom armors
- Modification of list of mineable objects
- Advanced configuration files