InfraRedstone is a mod designed to create a simpler but more capable version of redstone. While there are many other mods that do this, they mostly resort to systems that only have two states: on or off. InfraRedstone has a 64-value system that's flexible, light on servers, and easy to understand.
InfraRedstone is based off a Capability system, with only logic blocks as TileEntities; cables don't tick or even update, ever, providing a huge boost over vanilla redstone. There are built-in logic gates which are designed to work well with more than two signal values, and modules like the Shifter to use signals in ways no other system can.
For more information and to learn how to develop add-ons, see the InfraRedstone wiki.
