CurseForge
CurseForge is a platform for distributing Modded content for a number of different games, most notably Minecraft.
The Website
On CurseForge's website, you can discover Mods, ModPacks, Shaders, Data Packs, Resource Packs, Bukkit Plugins, Worlds, and even Bedrock Addons. Their search tool is great for finding what you need.
The Modded Launcher
CurseForge has a Launcher that supports Minecraft and other games.
However, we don't recommend using this Launcher due to its dependence on Overwolf, which is known to be spyware.
You can download the Launcher on its own without Overwolf if you choose, however, due to CurseForge's relation with Overwolf, we don't trust the standalone version.
Interesting info
The most downloaded Mod on CurseForge is Just Enough Items (JEI).
The most downloaded ModPack on CurseForge is RLCraft.
As of writing, CurseForge hosts 200k+ Minecraft Mods, with over 75 Billion downloads.