Stepmania is a simulator of what you may know as DDR (Dance Dance Revolution) or ITG (In The Groove). However, stepmania these days supports and is mostly played on a keyboard, which means that you don't need to buy a dance pad. The game also supports online play.
Gameplay
Arrows will scroll up in four different columns. When an arrow reach a certain bar you are supposed to hit the right key corresponding to the right column. Depending on how well you time the arrow you will receive a greater amount of points. If you miss or time the arrows badly your life bar will decrease. When it runs out you will lose, just like Osu!
Simfiles (beatmaps)
Just like Osu! you can create your own custom beatmaps, which are refered to as ”simfiles” in stepmania. There are serveral websites where you can share your works or download others':
Otaku's Dream (runs anime & other japan-related simfile pack projects. Recently released their 6th anime mix which is available to get here. You can find their YouTube channel here)
Bemanistyle (simfile database)
Flash Flash Revolution (flash version of stepmania, doesn't support custom simfiles. Also has a big sub-forum for stepmania which runs simfile pack projects from time to time)
Keybeat Online (another flash version of stepmania without custom simfile support. Runs simfile pack projects without any specified genre).
Zenius-I-Vanisher (stores the DDR packs and other pad simfiles)
There are big and popular websites which are more pad-oriented as well but I don't keep track of those.
You can download the game from: http://www.stepmania.com
If you want to play the game online then follow the instructions given here: http://www.stepmaniaonline.eu
Gameplay
Arrows will scroll up in four different columns. When an arrow reach a certain bar you are supposed to hit the right key corresponding to the right column. Depending on how well you time the arrow you will receive a greater amount of points. If you miss or time the arrows badly your life bar will decrease. When it runs out you will lose, just like Osu!
Simfiles (beatmaps)
Just like Osu! you can create your own custom beatmaps, which are refered to as ”simfiles” in stepmania. There are serveral websites where you can share your works or download others':
Otaku's Dream (runs anime & other japan-related simfile pack projects. Recently released their 6th anime mix which is available to get here. You can find their YouTube channel here)
Bemanistyle (simfile database)
Flash Flash Revolution (flash version of stepmania, doesn't support custom simfiles. Also has a big sub-forum for stepmania which runs simfile pack projects from time to time)
Keybeat Online (another flash version of stepmania without custom simfile support. Runs simfile pack projects without any specified genre).
Zenius-I-Vanisher (stores the DDR packs and other pad simfiles)
There are big and popular websites which are more pad-oriented as well but I don't keep track of those.
You can download the game from: http://www.stepmania.com
If you want to play the game online then follow the instructions given here: http://www.stepmaniaonline.eu