Games like Cell #31
Games like Cell #31 include Bit Blaster XL, Chippy, Assault Android Cactus+, Waves, and Nova Drift. We matched them by the tags players give Cell #31 on Steam (Bullet Hell, Shoot 'Em Up, Twin Stick Shooter, Arcade, and Difficult): closest matches first, and among equally close ones the better-known games.

Bit Blaster XL
Shared: Bullet Hell · Shoot 'Em Up · Difficult

Chippy
Shared: Bullet Hell · Twin Stick Shooter · Shoot 'Em Up

Assault Android Cactus+
Shared: Bullet Hell · Shoot 'Em Up · Twin Stick Shooter

Waves
Shared: Bullet Hell · Shoot 'Em Up · Twin Stick Shooter

Nova Drift
Shared: Bullet Hell · Shoot 'Em Up · Arcade

Planes, Bullets and Vodka
Shared: Shoot 'Em Up · Bullet Hell · Arcade

Nex Machina
Shared: Bullet Hell · Twin Stick Shooter · Arcade

Enter the Gungeon
Shared: Bullet Hell · Difficult · Twin Stick Shooter

Sky Force Reloaded
Shared: Shoot 'Em Up · Bullet Hell · Arcade

Ikaruga
Shared: Bullet Hell · Shoot 'Em Up · Arcade

Beat Hazard
Shared: Bullet Hell · Twin Stick Shooter · Shoot 'Em Up

LUFTRAUSERS
Shared: Bullet Hell · Arcade · Shoot 'Em Up

BALL x PIT
Shared: Bullet Hell · Arcade · Shoot 'Em Up

Revolution Ace
Shared: Shoot 'Em Up · Bullet Hell · Shooter

Geometry Wars: Retro Evolved
Shared: Twin Stick Shooter · Arcade · Bullet Hell

Geometry Wars™ 3: Dimensions Evolved
Shared: Twin Stick Shooter · Shoot 'Em Up · Bullet Hell

ZeroRanger
Shared: Shoot 'Em Up · Bullet Hell · Arcade

Sektori
Shared: Shoot 'Em Up · Twin Stick Shooter · Arcade

Vampire Survivors
Shared: Bullet Hell · 2D · Arcade

Furi
Shared: Bullet Hell · Shoot 'Em Up · Difficult

Star Saviors
Shared: Bullet Hell · Shoot 'Em Up · Arcade

Mushihimesama
Shared: Bullet Hell · Shoot 'Em Up · Arcade

Touhou Koumakyou: New Classic - the Embodiment of Scarlet Devil
Shared: Bullet Hell · Shoot 'Em Up · Difficult

Star of Providence
Shared: Bullet Hell · Shoot 'Em Up · Difficult