Great Big World is a collection of mods packaged & integrated together with the goal of reimagining Minecraft under new design philosophies. It's a modern take on the "alternate timeline" genre most notably seen in Better Than Adventure and Not So Secret Saturday.
Check out the Gallery or the showcase videos on YouTube for a better look!
To check out project progress, where it's headed, & known bugs, see the Project Roadmap!
Great Big World will never require another mod to install (aside from Fabric API, of course). It is organized into multiple sub-mods, which are all packaged together into a single mod file:
Great Big World caters both to players who want to enjoy the classic simple, sandboxy, survival Minecraft from years ago, and to players who prefer the more complex, progressive game it is now.
For the former, Great Big World strips the Overworld dimension of many features that are deemed unnecessary or bloaty. This includes many structures, biomes, and even natural blocks such as Granite, Diorite, & Andesite. Overall, the Overworld is more akin to old Minecraft. Critically, however, Ancient Cities remain in the Overworld as a core part of dimensional progression.
For the latter, Great Big World adds a new "alternate" dimension predictably called the Alterworld. This dimension retains features of modern Minecraft & many old ones as well, such as Villages, Copper, Cherry Groves, & variant mobs. This dimension will recieve numerous content updates during Phase 2 of the mod, including biomes, structures, mobs, blocks, etc.
Players start in the Overworld. There are 2 methods of entering the Alterworld, 1 temporary & 1 permanent:
Above is the core dimensional progression for players. The Nether & the End retain their position in this path. There will be 2 more dimensions implemented in the future that can be considered "horizontal" progression, as they will not be necessary to "beat the game".
The Alterworld V1 is currently just vanilla Minecraft with general tweaks from the mod as a whole. V2 will contain many new biomes, structures, mobs, etc. This will be worked on once the mod passes Phase 1 (see the Roadmap). V3 of the Alterworld will give it dynamic systems, such as civilizations, quests, & player interactivity. At that point, the dimension will be considered complete.
Probably not, but I'll consider it on a case-by-case basis. Please note that Great Big World has an ARR license, which does not allow redistribution (which includes using it in modpacks) without permission from its author (me).
The issue with using GBW in modpacks relates to FAQ #1: there is no guarantee that GBW will be compatible with other content mods. If it were free to use in modpacks, I would be flooded with bug reports on compatibility issues that I've explicitly stated will not be fixed. If you wish to use GBW in a modpack, please contact me directly and I will make a decision. As a general guideline, if your pack otherwise consists of non-gameplay mods, GBW will be allowed. If it contains a large number of other content mods, it will not. The pack must be focused around GBW, because that is the mods intent. It's a standalone experience.
From version 0.15.0 onwards, GBW now embeds separated standalone mods in its jar file. These mods are designed to be utilized outside of GBW and are free to be used in modpacks. Please see these mods' pages to play with them separately & to use them in modpacks.
Not anytime soon, & more than likely never. The mod is massive & will only continue growing. It does & will rely on capabilities provided by modern Minecraft versions. Any backport will require a huge time cost, when I could use that time to continue developing towards the overarching goal.

An alternate timeline mod for modern Minecraft