Each game mode has its own icon/symbol: (osu!, osu!taiko, osu!catch, and osu!mania respectively).
The default game mode is osu!. However, upon start-up, osu! will open with the game mode that was last selected. To switch between game modes, the player can either click on the
Mode button at the bottom of the Song Selection screen, or by pressing
4 to switch between osu!, osu!taiko, osu!catch, and osu!mania respectively.
Mode selection interface
Main page: osu!
osu! (commonly referred to as osu!standard) is the default game mode in the osu! client, and is based on the original iNiS' rhythm video game Osu! Tatakae! Ouendan. In osu!, the player is expected to tap hit circles, hold sliders, and spin spinners to the beat of songs.
Main page: osu!taiko
osu!taiko is based on the Taiko no Tatsujin game series produced by Bandai Namco Entertainment. Made to mimic the feel of playing a real drum, the player makes use of a keyboard or drum kit to hit differently-colored circles on a single conveyor.
Main page: osu!catch
osu!catch is loosely based on a minigame inside of a Beatmania simulator, which itself is believed to be based on the EZ2CATCH mode from the EZ2DJ series. The game mode consists of falling fruit of differing varieties and a "catcher" holding a plate to catch the fruit.
Main page: osu!mania
osu!mania is based on a variety of conveyor-type rhythm games (namely Dance Dance Revolution and Beatmania). The game mode was chiefly introduced and implemented by woc2006, and is made to mimic the feel of a real piano through the use of keyboard keys.