These are 3 patches for Pokemon Emerald (US). The 3 .zip files are the source codes for each hack, meant for if you intend to use these hacks as a base.
Here is a brief description of each patch:
The bugfixes patch just changes bugs and glitches in the original game.
PE PLUS introduces minor QOL changes, mostly ported from the newer games. The general moment-to-moment gameplay shouldn't be affected much.
PE DOUBLE PLUS introduces more substantial changes. It modifies battle mechanics to match Gen VIII. Additionally, it introduces the toggleable Exp. Share, infinite TMs, and chain fishing from Gen VI

PE PLUS is designed to be an improved version of the original while not changing the gameplay at all. Hypothetically, PE PLUS is just like the original, just better in subtle ways that would make it the definitive version.
PE DOUBLE PLUS is designed to go beyond PE PLUS and doesn't aim to be the definitive version. It aims to be an updated version of the main game but is different enough that it doesn't ever replace the original experience.
Use whichever patch suits your tastes.

You can confirm that your rom is properly patched by checking the settings of the game. If the default border is border 20, then the game is patched.
You can confirm which version of the patch you are using by which Pokemon Professor Birch summons in the introduction.
Bugfixes: Trapinch
PE PLUS: Vibrava
PE DOUBLE PLUS: Flygon

Bugfixes (all courtesy of the original Pokemon Emerald Disassembly unless otherwise noted):
This patch only fixes some bugs in Pokemon Emerald.
-Properly seeds the RNG (This just means random numbers are more random)
-When diving on route 125, the route name display now correctly says route 125, not route 129
-Fixes the Pomeg berry glitch
-Fixes the dive glitch
-Fixes the pokeblock throw glitch
-Fixes a glitch where your Battle Pike and Battle Factory win streaks are incorrectly reported to the player
-Fixes a glitch where HP and Defense IVs were less likely to be inherited by an egg
-Fixes a bug in the contest AI
-Fixes a bug where not every Pokemon in a doubles Battle Tower challenge would receive a ribbon
-Fixes a bug when fighting Steven where his Pokemon were assigned the wrong natures
-Fixes a bug where if a roaming Pokemon used roar, they would stop roaming
-Fixes a bug where Battle Dome trainers would have weaker Pokemon
-Fixes a bug where Battle Dome trainers would have an unintentional advantage when the round ends in a draw
-Fixes multiple Trainer AI bugs
-Fixes an issue where the Battle Maniac wouldn't recognize when the player had received the Gold Pike Badge
-Fixes an issue where the game wouldn't allow the player to reset the RTC from the main menu
-Fixes a graphical issue when dismounting a surfing Pokemon into a patch of grass
-Fixes an issue where battle factory opponent IVs are determined by Battle tower win streak in the base game (Scylaceus)
-Not a bug, but the default settings were changed to what the average user would most likely default to (Mkol03)
-Not a bug, but a higher quality sound mixer is included by default (itapix)
-Not a bug, but the user can now skip pauses in battle by pressing the A or B button (Mkol03)

PE PLUS:
All aforementioned changes, plus new QOL improvements
-You can now evolve trade-only Pokemon without trading (Mkol103) (See chart below)
-Battles move quicker, and mid-battle notifications trigger when abilities are activated (RHH)
-The HP bars move faster (SonikkuA-DatH)
-Text moves faster. The "mid" text option now moves as quickly as the previous "fast" option (Ella_trifle)
-The stats which a nature improves or weakens are colored red and blue respectively on the Pokemon status screen (DizzyEgg)
-When naming something, the keyboard automatically switches from uppercase to lowercase (Jaizu)
-When a repel runs out, you are prompted to use a new one (Exposeed)
-When you use medicine, you are allowed to use it again (Ghoulslash)
-Day now begins at 6 AM, night begins at 6 PM (in Emerald, day begins at 12 AM, night begins at 12 PM) (BuffelSalt)
-When the player whites out, the money loss calculation is taken from newer games. (Lunos)
-Pokemon can now forget HM moves without the move deleter (Lunos)
-Everstones now let eggs inherit natures from their parent (Robinlukke & takyon)
-Routes where it is raining do not need their berries watered for maximum yield (Buffel Salt)
-The summary screen for Pokemon now wraps around (Zeturic)
-You can now see the type and strength of Hidden Power on the summary screen (Jirachi & Lunos & Sapphire Jester)
-Check your PC for some Mysterious Gifts (MKol103)

PE DOUBLE PLUS:
All aforementioned changes, and new, more noticeable changes
-The physical/special split is implemented (RHH)
-Fairy type is implemented (RHH)
-All battle mechanics are updated to match their Gen VIII counterpart (Critical capture, no badge boost, changed critical hit chance, new exp gain formulas, new status damage calculation, etc.) (RHH)
-Chain Fishing from Gen VI has been ported over (Ghoulslash)
-All TMs are infinite use (Paccy & Lunos)
-Sitrus Berries now heal 1/4 of HP like in newer gens (Ketsuban & Eatthepear)
-Poisoning now doesn't faint Pokemon on the overworld, but leaves them with 1 HP like in newer games (Lunos & Blurose)
-The Experience Share item is now toggleable rather than being a hold item (Lunos & Blurose)
-The bike can now shift between Mach and Acro by pressing the R-button (Lunos & Blurose)

Evolution chart:
Poliwhirl -> Politoed (Level up while holding King's Rock)
Kadabra -> Alakazam (Level 37)
Graveler -> Golem (Level 37)
Machoke -> Machamp (Level 37)
Slowpoke -> Slowking (Use a Water Stone)
Haunter -> Gengar (Level 37)
Onix -> Steelix (Level up while holding a Metal Coat)
Seadra -> Kingdra (Level up while holding Dragon Scale)
Scyther -> Scizor (Level up while holding Metal Coat)
Porygon -> Porygon2 (Level up while holding Up Grade)
Clamperl -> Huntail (Level up while holding DeepSeaTooth)
Clamper -> Gorebyss (Level up while holding DeepSeaScale)

All patches are authored by Mkol103