CoFHLib mod 1.12.2, 1.11.2 is a library mod that designed to boot other mods made by CoFH Team. Now it is replaced by CoFH Core, but some older mods still require CoFH Lib to run, as they cannot use CoFh Core or the creators may have stopped their developments.
At the early day of CoFH Team, there was only 1 man to develop, maintain as well as update all the mods. CoFH Lib was created so that all mods of CoFH Team would have the same source code, making upgrading and maintaining more convenient. With its simple design, CoFH Lib was praised and widely used in large mods like Simple Jetpack, MineChem or Calculator, which completely change gameplay by adding new rules and scientific knowledge into the game.
Due to the constant development of Minecraft, as well as the astounding success of Thermal mod packs (including Thermal Foundation, Thermal Expansion and Thermal Dynamics), CoFH Team grown in terms of manpower. It was also the time that the developer decided to give the Thermal mods pack a new change, so they made CoFH Core which contains latest technologies and ground-breaking functions. As the result, CoFH Lib slowly being forgotten, but big mods like Simple Jetpack or Minechem still use it up to now. To use Minechem and Simple Jetpack, you will need CoFHLib installed with Minecraft 1.7.10 and Forge Mod Loader.
How to Install CoFHLib Mod 1.12.2, 1.11.2 with Forge