Games like Alien Together
Games like Alien Together include Paddle Paddle Paddle, Chained Together, Overcooked! 2, Ultimate Chicken Horse, and Gang Beasts. We matched them by the tags players give Alien Together on Steam (Casual, Parkour, Racing, Indie, and Singleplayer): closest matches first, and among equally close ones the better-known games.

Paddle Paddle Paddle
Shared: Casual · Co-op · Parkour

Chained Together
Shared: Co-op · Casual · Platformer

Overcooked! 2
Shared: Co-op · Casual · Local Co-Op

Ultimate Chicken Horse
Shared: Platformer · Local Co-Op · Party Game

Gang Beasts
Shared: Co-op · Casual · Singleplayer

SpeedRunners
Shared: Racing · Indie · Platformer

PICO PARK
Shared: Co-op · Casual · Online Co-Op

Bloons TD 6
Shared: Co-op · Casual · Singleplayer

Trine 2: Complete Story
Shared: Co-op · Action-Adventure · Platformer

Climber Animals: Together
Shared: Casual · Co-op · Platformer

BattleBlock Theater®
Shared: Co-op · Platformer · Local Co-Op

Super Bunny Man
Shared: Co-op · Platformer · Singleplayer

It Takes Two
Shared: Co-op · Local Co-Op · Online Co-Op

Brawlhalla
Shared: Casual · Co-op · Platformer

Sonic Racing: CrossWorlds
Shared: Racing · Co-op · Singleplayer

Liars Bar
Shared: Casual · Co-op · Indie

Haste
Shared: Parkour · Racing · Singleplayer

Only Up: With Friends
Shared: Casual · Parkour · Co-op

Golf With Your Friends
Shared: Casual · Indie · Co-op

Party Animals
Shared: Casual · Co-op · Party Game

MECCHA CHAMELEON
Shared: Casual · Party Game · Co-op

Cuphead
Shared: Co-op · Platformer · Indie

How to Fish
Shared: Co-op · Indie · Online Co-Op

Split Fiction
Shared: Co-op · Action-Adventure · Local Co-Op