Games like Danmaku Unlimited 3
Games like Danmaku Unlimited 3 include ZeroRanger, Ikaruga, Star Saviors, LUFTRAUSERS, and Nova Drift. We matched them by the tags players give Danmaku Unlimited 3 on Steam (Bullet Hell, Shoot 'Em Up, Action, Indie, and Arcade): closest matches first, and among equally close ones the better-known games.

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

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

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

LUFTRAUSERS
Shared: Bullet Hell · Indie · Action

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

Nex Machina
Shared: Bullet Hell · Action · Arcade

BALL x PIT
Shared: Action · Bullet Hell · Arcade

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

Savant - Ascent
Shared: Action · Indie · Shoot 'Em Up

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

Touhou Tenkuushou ~ Hidden Star in Four Seasons.
Shared: Bullet Hell · Shoot 'Em Up · Great Soundtrack

Touhou Fuujinroku ~ Mountain of Faith.
Shared: Bullet Hell · Action · Indie

BLUE REVOLVER
Shared: Bullet Hell · Shoot 'Em Up · Action

UBERMOSH
Shared: Action · Indie · Arcade

Touhou Kouryudou ~ Unconnected Marketeers.
Shared: Bullet Hell · Shoot 'Em Up · Action

Touhou Kikeijuu ~ Wily Beast and Weakest Creature.
Shared: Bullet Hell · Indie · Shoot 'Em Up

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

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

Jet Lancer
Shared: Action · Indie · Shoot 'Em Up

TouHou Makuka Sai ~ Fantastic Danmaku Festival Part II
Shared: Bullet Hell · Shoot 'Em Up · Indie

Vampire Survivors
Shared: Bullet Hell · Indie · Action

TouHou Makuka Sai ~ Fantastic Danmaku Festival
Shared: Bullet Hell · Action · Indie

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

Super Galaxy Squadron EX Turbo
Shared: Bullet Hell · Shoot 'Em Up · Action