I've been fascinated by Io ever since reading _why's two introductory posts on it:

* http://web.archive.org/web/20080212010904/http://hackety.org...

* http://web.archive.org/web/20080430135919/http://hackety.org...

See also Ioke, a JVM- and CLR-based language heavily inspired by Io, being developed by JRuby developer Ola Bini:

http://ioke.org/