Well, "open source" super heroes anyway. Inspired by the recent discovery of Jenny Everywhere, aka "The Shifter," the first such character, Michael Dean and Kelle Sande are releasing several characters they created for anyone to use. We're putting them up, along with Jenny, on the Public Domain Super Heroes website.
The first three are up now - The Outworlder,
Free for use by all, with the only stipulation being that you should to include this paragraph:
"The characters of The Outworlder, Jackpott, & Cyber-Knight are available for use by anyone, with only one condition. This paragraph must be included in any publication involving these characters, in order that others may use these properties as they wish. All rights reversed."