Pokémon Emerald Horizons

Features
Many of the features below are either inherent in the RHH's pokeemerald-expansion branch or possible due to the tireless work of the contributors in the Simple Modifications Directory (credited at the bottom of the post)!
The key features of this game include:

Difficulty Related: Set Mode, Level Caps, and Disabled Battle Bag
Most Gen 1-8 Pokémon are obtainable, including Hisuian forms
Modern Battle Engine, with Fairy-Type, Mega Evolution, Updated Moves, and Physical/Special Split
Loads of optional boss battles, with 8 Kanto Gym Leaders, 8 Johto Gym Leaders, and a few miscellaneous bosses who reward valuable items
Exp. All
Bosses and mid/late game Trainers scale to or relative to your strength, so grinding/overleveling isn't a factor
Updated move animations, courtesy of Skeli and ghoulslash
No EVs/IVs/Natures factored into stats
75 TMs, with about 50% vanilla TMs and 50% custom TMs
Ghoulslash's DexNav (12 unique land/5 unique surf/5 unique fishing encounters); hold A to creep!
PSF's Quest Menu UI, with 30 Side Quests to Complete
Buffel's Poké Vial implementation
Ghoul's Item Description Headers
Badge-Based Poké Marts
Cut, Rock Smash, Strength, Surf, and Waterfall don't need to be taught to progress
Level Cap Window updates as you progress
No more annoying fishing minigame
BW Repel System
Unlimited use TMs/Forgettable HMs
Nicknaming and Move Relearning in Party Screen
Decapitalization
Slateport City Level Grinder to quickly hit Level Cap
Linking Cord for most trade related evolutions
Post-Game Boss Rush Mode
2.5x Lucky Egg
Premier Ball Bonuses
No poison damage in the overworld