Engine

Engine can refer to one of many energy-producing machines in the game. Different mods have engines that function in different ways than that of other mods.

BuildCraft

 * Redstone Engine
 * Stirling Engine, formerly known as Steam Engine
 * Combustion Engine

Forestry

 * Peat-fired Engine
 * Biogas Engine
 * Electrical Engine
 * Clockwork Engine

Railcraft

 * Hobbyist's Steam Engine
 * Commercial Steam Engine
 * Industrial Steam Engine

Thermal Expansion

 * Steam Engine, not to be confused with Railcraft's Steam Boiler machine
 * Magmatic Engine

Gravitation Suite

 * Gravitation Engine - Does not produce energy, but is a component of the GraviChestPlate

Steve's Carts
These are modules that power custom-built carts:
 * Tiny Coal Engine
 * Coal Engine
 * Basic Solar Engine
 * Solar Engine