Developer: several developers.

Forge for 1.1

Forge for 1.2.5:

Forge for 1.3.2:

Forge for 1.4.7:

NOTES: you can find forge for other various versions of minecraft by looking on the TAB menu on the LEFT of the screen @ the websites listed above. This is just an easy reference page to find the Forge version your looking for that will work with MC versions 1.1 thru 1.4.7

This is the BASIC mod that you need to download to cause any other minecraft mod to work.
Every mod to minecraft works off of this mod.
This mod once downloaded will alter your .minecraft folder to now include a 'MODS' folder.
you then put any minecraft mods you want to download and use into THAT folder.
Adding mods to your minecraft game is not hard.But, its not simple either.
With a little patience and well.. by watching a few videos on youtube about how to
add mods to minecraft. You can learn it easily enough. :)
FORGE as been around since the DAWN of mincraft modding. every since minecraft version 1.1
You can find the older versions of FORGE for minecraft by going to there offical page
on at the link above. Make sure you download the recommended FORGE version for YOUR
version of minecraft that your playing on.