It seems there are at least 16 different artists under the name IO.
1) Io was a emotive hardcore punk band from Pittsburgh, Pa, who released a full length and 7" on Hope Records/Hard Travelin and existed from 2001 to 2003 but played a reunion show in 2005.
2) IO is a mostly instrumental, post-metal, math rock quartet from Birmingham, UK. Website.
3) Two talented music fans and DJ's are behind Ukrainian house music act 'iO': Alex Voznichenko and Artem Zhovtobriukh. Project launched in februari 2009 and since then gained attention from major house music jocks such as Joris Voorn and Bart Skils. (myspace.com/ioukraine)
4) IO is a 4 releases cheap records inhouse project with Erdem Tunakan, Patrick Pulsinger, Gerhard Potuznik and Umberto Gollini.
5) "iO" is the band formed by 3 of the 4 previous Guano Apes members (without singer Sandra Nasic) and singer Charles Simmons. Official homepage.
6) Io was a melodic death metal band from Nurmijärvi, Finland.
7) Io is a black metal band from the United States of America.
8) iO is the drum and bass DJ/producer from Minsk, Belarus.
9) io was an American rock band from North Carolina, relocated to San Francisco, CA, active from 2001-2005. Released the album "Where The Engines Lay" in 2003, Later renamed Dear Kerosene(2005-2006).
10) Io is an artist from Bellingham, WA who makes digital instrumental music and contributes to a pair project with Jon Spinelli called House of Leaves.
11) IO is an Experimental-Industrial/Terror-Noise group from Berlin, Germany.
12) Io is drone/ ambient project of Jonas Laster (see also Father Io)
13) Io is an Austrian busker
14) Io is a experimental-ambient project based in Miami, then Washington, DC, then Toronto, and now in Miami again. Releases on Elegua Records include "Little Haiti Suite," "The Fat Albert Concert," and "Live @ the Ambient PiNG, Vol. 1."
15) IO (Inside Ocean) is a hungarian producer, Mátyás Milkovics's solo production. [url=http://www.facebook.com/pages/IO/140447772669720[/url].
16) Io is an instrumental progressive metal / djent / fusion project by an unknown artist from New York. A 6 song self-titled EP was released on February 27th, 2012 on Bandcamp, currently available for free download.