Afterbeat (Project Arrhythmia)

"Afterbeat" is a musical bullet-hell in which all things beautiful are deadly. A cacophony of lights, music, pulses and blocks, Afterbeat features tight bullet-hell style gameplay where up to 4 players in local co-op must navigate their way through evolving scenes and obstacles, all timed to the beat.
STORY
Set in 207X, a mysterious disease called "LMNS" has been ravaging the world. A lone Chiral researcher, Anna Schroeder, attempts to find the cure with her trusty supercomputer companion HAL. Stumbling upon various “Projects,” the duo decides to investigate the efficacy of a cure using a pulse/rhythm-based interface.
CURRENT FEATURES
Complete Story Mode: Over 20+ hand-crafted, heart-pounding levels interwoven with an engaging story.

Dodge The Beat: Stages consist of mesmerizing, musically timed scenes, each one telling a story. Feel the rhythm and feel your way around the hazards! Anna will judge how you do.

Challenge Your Friends: Up to 4 players supported in local co-op mode.

Robust Level Editor: A carefully designed level editor allows users to create their own levels and challenges using whatever music they wish.

Huge Community: A Wealth of user-created content exists, fully integrated into the game through the usage of the level editor and user-made levels. Already, 2000+ community levels have been uploaded, and more are being made daily.

Some screenshots used are from UGC:
Sleep Cannon by cozm

Excelsus by DXL44

Lucid by Taikeb0

This game was previously named "Project Arrhythmia."