Games like Appalachian Onslaught
Games like Appalachian Onslaught include Hades, Hades II, Shape of Dreams, Megabonk, and Dead Cells. We matched them by the tags players give Appalachian Onslaught on Steam (Action Roguelike, Hack and Slash, Roguelite, Tower Defense, and Auto Battler): closest matches first, and among equally close ones the better-known games.

Hades
Shared: Action Roguelike · Hack and Slash · Roguelite

Hades II
Shared: Roguelite · Hack and Slash · Action Roguelike

Shape of Dreams
Shared: Action Roguelike · Hack and Slash · Roguelite

Megabonk
Shared: Action Roguelike · Roguelite · Roguelike

Dead Cells
Shared: Action Roguelike · Roguelite · Roguelike

Skul: The Hero Slayer
Shared: Action Roguelike · Roguelite · Roguelike

Astral Ascent
Shared: Action Roguelike · Hack and Slash · Roguelite

Soulstone Survivors
Shared: Action Roguelike · Roguelite · Hack and Slash

Deadzone: Rogue
Shared: Roguelite · Roguelike · PvE

Halls of Torment
Shared: Action Roguelike · Roguelite · Roguelike

Lost Castle
Shared: Action Roguelike · Hack and Slash · Roguelite

Mortal Sin
Shared: Action Roguelike · Hack and Slash · Roguelite

Vampire Survivors
Shared: Action Roguelike · Roguelite · Roguelike

Cinderia
Shared: Action Roguelike · Hack and Slash · Roguelite

Death Must Die
Shared: Action Roguelike · Roguelite · Hack and Slash

Moonlighter
Shared: Hack and Slash · Roguelite · Action Roguelike

Ravenswatch
Shared: Action Roguelike · Roguelike · Roguelite

Risk of Rain 2
Shared: Action Roguelike · Roguelite · Roguelike

Windblown
Shared: Action Roguelike · Hack and Slash · Roguelite

Monsters are Coming!
Shared: Roguelite · Tower Defense · Action Roguelike

CloverPit
Shared: Roguelite · Roguelike · Strategy

Gunfire Reborn
Shared: Roguelite · Roguelike · Action Roguelike

Jotunnslayer: Hordes of Hel
Shared: Action Roguelike · Roguelite · Hack and Slash

SWORN
Shared: Roguelite · Action Roguelike · Hack and Slash