Geometry Dash

Geometry Dash is a rhythm-based platform game developed and published by RobTop Games. It started being sold for two dollars on August 13, 2013. It is a 2D platform game that involves dodging geometric obstacles (spikes, walls, and creatures) in a series of levels that you can complete. You can also create your own levels in the editor, and play levels made by other people. To finish levels, you have to get through the whole level without dying. You can collect items such as coins, stars, orbs, and diamonds. There are different vehicles in the game.
Gameplay.
The player uses the keyboard, touch screen, controller, or mouse (depending on what device they are using) to jump over obstacles in each level. The primary goal of each level is to complete the level without dying. If the character dies you are sent back to the beginning of the level. There are other goals such as collecting currencies such as coins, stars, orbs, or diamonds. 
There are 21 main levels. 3 of them are demon levels which can be unlocked by collecting coins hidden throughout the levels. As of January 2023, there are 88 million levels made by other people.
Currency in Geometry Dash can range from being easy to hard to collect. Ways to collect currency are by completing quests for diamonds and completing map packs for secret coins and stars. Beating popular levels will give you orbs and will unlock user coin achievements if you collect the user coins.
Icons are a way of customizing your character. You can get icons by completing quests, achievements, and cracking vaults.
There are 3 different vaults in Geometry Dash. The original Vault requires 10 user coins, The Vault of Secrets requires 50 diamonds, and the Chamber of Time requires the Master Emblem. (sold in Scratch's Shop that requires 500 diamonds) Just like the Icon section, you can unlock different icons by secret codes in the vault.
The level editor uses different blocks, spikes, and decorations for you to add and create to your very own level. The level editor also allows you to do different things for a level. Background color changing, invisibility, movement triggers, and different variety of changes to your level creation. Update 2.1 added multiple different things to the level editor. Including dash orbs, the new spider vehicle, and a new orb, a push-down orb that is black.
Spinoffs.
RobTop released a number of spinoffs for the game, the first being Geometry Dash Lite, a demo version of the game without a level editor or many of the game's levels and icons. He then released Geometry Dash Meltdown, a teaser for GD 2.1 in 2015, Geometry Dash World, a teaser for 2.2 in 2016, and finally, Geometry Dash SubZero, another teaser for 2.2 in 2017.