This is more than a mod -- it is an entire API. You definitely need Minecraft Forge if you want your mods to work well. Some mods even require you to have Forge pre-installed before setting up other mods.
Here is the latest version officially presented by the open source community for all your Minecraft modification needs.
If you are looking for some other types of mods for Minecraft 1.11, then be sure to let us know in the comments section below.