Games like Fleet Summoner
Games like Fleet Summoner include Vampire Survivors, Banana, Cookie Clicker, Timberman, and TBH: Task Bar Hero. We matched them by the tags players give Fleet Summoner on Steam (Casual, Arcade, Hack and Slash, Idler, and 2D): closest matches first, and among equally close ones the better-known games.

Vampire Survivors
Shared: Pixel Graphics · 2D · Casual

Banana
Shared: Casual · 2D · Idler

Cookie Clicker
Shared: Casual · Idler · Pixel Graphics

Timberman
Shared: Casual · Pixel Graphics · Arcade

TBH: Task Bar Hero
Shared: Idler · Pixel Graphics · Casual

To The Core
Shared: Casual · Arcade · 2D

Melvor Idle
Shared: Casual · Idler · 2D

Cyberhunt
Shared: Casual · Arcade · Indie

Shelldiver
Shared: Casual · Arcade · Idler

Space Rock Breaker
Shared: Casual · Arcade · Idler

Nodebuster
Shared: Casual · Idler · Arcade

Deep Space Cache
Shared: Casual · Idler · Indie

Keep on Mining!
Shared: Casual · Idler · Arcade

Bit Blaster XL
Shared: Arcade · Casual · 2D

Boneraiser Minions
Shared: Pixel Graphics · 2D · Casual

Orbitmine
Shared: Arcade · Casual · Sci-fi

Death Must Die
Shared: Pixel Graphics · Hack and Slash · 2D

A Game About Feeding A Black Hole
Shared: Casual · Idler · 2D

LUFTRAUSERS
Shared: Arcade · 2D · Pixel Graphics

Shower With Your Dad Simulator 2015: Do You Still Shower With Your Dad
Shared: Arcade · Casual · 2D

Megabonk
Shared: Indie · Arcade · Pixel Graphics

Brotato
Shared: Singleplayer · Bullet Hell · Hack and Slash

Planes, Bullets and Vodka
Shared: Casual · Arcade · 2D

Razortron 2000
Shared: Casual · Arcade · Indie