is a game where everything is cubes, except the things that aren't cubes.
"Mods" is short for "modifications" and refers to edits made to a game, often to add more content. In the context of Minecraft, the first mods replaced certain class files inside minecraft.jar with modified versions. It was quickly discovered that this led to conflicts where two mods couldn't be installed together because they both needed to overwrite the same file. This quickly led to the development of frameworks, or modloaders which make these edits once, centrally, connecting them to one or more other installed mods. Soon after that, it became normal for mods to not edit any class files, as all needed edits were included in the modloader. Mods could then be installed by dropping them into a separate mods folder with no need to edit minecraft.jar for each mod. This is why most mods are distributed as .jar files, which a player could download into their mods folder with no additional setup needed.
In the past, I wrote a bunch of Minecraft mods. This set of mods is now referred to as "series 1". Download links can be found here, but not a lot of information.
⚠ License change: Series 1 files are mostly provided under the terms of AGPLv3 with certain exceptions, though it varies per file and each file is tagged with its own license which can be viewed by opening the file. You're still allowed to make modpacks and edits, but make sure to follow the new terms. ⚠
Group 6 is mods created for modjams which are not and were never maintained: Chicken Bones, SpinnyThingsCraft, Totally Random Surgery, Captchalogue Sylladex, Just Blood Carts, Homestuck Loading Screen, The Slab Also Siren Head, and Hypoloop.