Records of osu!'s history, all in the osu! wiki.

  • 2007 - Initial game build
  • 2008 - Taiko and Catch the Beat, more mods, and major improvements
  • 2009 - osu! iPhone
  • 2010
  • 2011 - osu! wiki
  • 2012 - Five years of osu!, osu!mania, widescreen support, and visual settings
  • 2013 - UI overhaul, HD skins, (more) widescreen support, osu!mania editor, in-game collections, moddingV2 was introduced, Disqus, osu!api, accuracy overlays, Comic Fiesta 2013, downloads unrestricted*, and osu!cuttingedge (osu!supporters only)
  • 2014 - BPM scrolling, in-game intro/outro sequences, osu!cuttingedge (for everyone*), and snow!
  • 2015 - jizz (redesigned osu!web), osu!weekly, and osu!coins
  • 2016 - scorev2, open-source osu! announced (osu!lazer), and osu! wiki (overhaul)
  • 2017 - first osu!lazer build release, and Discord integration
  • 2018 - ?

On a side note, the osu! wiki has a bit of its own detailed history in and of itself.