Games like Nordenfelt
Games like Nordenfelt include Vampire Survivors, LUFTRAUSERS, Zombotron, Skul: The Hero Slayer, and Star Saviors. We matched them by the tags players give Nordenfelt on Steam (Action, Indie, Singleplayer, Shoot 'Em Up, and 2D): closest matches first, and among equally close ones the better-known games.

Vampire Survivors
Shared: Indie · Bullet Hell · 2D

LUFTRAUSERS
Shared: Indie · Action · Bullet Hell

Zombotron
Shared: Action · Indie · 2D

Skul: The Hero Slayer
Shared: Action · Indie · 2D

Star Saviors
Shared: Action · Shoot 'Em Up · Indie

DRAINUS
Shared: Action · Indie · Shoot 'Em Up

ZeroRanger
Shared: Indie · Shoot 'Em Up · Action

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

Touhou Fuujinroku ~ Mountain of Faith.
Shared: Action · Indie · Shoot 'Em Up

Cyberhunt
Shared: Action · Indie · Shoot 'Em Up

Revolution Ace
Shared: Action · Indie · Shoot 'Em Up

Intrusion 2
Shared: Action · Indie · 2D

Bright Memory: Infinite
Shared: Action · Indie · Singleplayer

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

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

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

ICEY
Shared: Action · Indie · Singleplayer

Hollow Knight: Silksong
Shared: Indie · Singleplayer · 2D

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

Planes, Bullets and Vodka
Shared: Action · Shoot 'Em Up · Singleplayer

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

Star of Providence
Shared: Indie · Shoot 'Em Up · Action

The Bug Butcher
Shared: Action · Indie · Shoot 'Em Up

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