Upgrade
Almost every game played online for free this way or another includes upgrades. They can relate weaponry, life, armor, deadly power of your hero, and his/her special abilities. Or weaken monsters. But there are such games, which made the upgrade system an inalienable part of the process and made it necessary to make too often. Like, after each level (every several minutes or sooner). This is the case in launching rockets – they should fly high but without improvements, they will simply show the same result. Or like flying through the distance – only improvements will make you get better results without standing still.
Free online games - Upgrade games
Upgrade games

Tube Clicker
68

Jetpack Joyride
72

Bounzy Online
63

Fastlane Road to Revenge Online
74

X Trial Racing
69

Road of Fury: Desert Strike
67

Bob the Robber 4
71

Burger Clicker
73

Vikings War of Clans
72

Knights Diamionds
69

Endless Truck
68

KULI
71

Idle Evolve
57

Poop Clicker 2
68

Paper Minecraft
71

Forge of Empires
70

Wanderers.IO
64

Ben 10 Upgrade Chasers
86

Tuber Simulator Online
70

Gone Fishing
73

Mad Digger
69

Bloons Tower Defense 5
70

Battles of Sorogh
65

Stickman vs Zombies
81

Stormfall: Age of War
71

Gold Miner
71

King of Thieves
72

Cyber Hunter
64

Heroic Quest
73

Police vs Thief: Hot Pursuit game
71

Stickman Shooter
63