it would be great if every language on their home page, as well as listing how to do common things such as this:

http://www.iolanguage.com/scm/io/docs/IoTutorial.html

would also give a demonstration of what makes this language unusual (beyond syntax).

for io it seems like this might be some smalltalk-inspired message passing stuff:

http://www.iolanguage.com/scm/io/docs/IoGuide.html#Objects-F...

combined with concurrency:

http://www.iolanguage.com/scm/io/docs/IoGuide.html#Concurren...

but it's hard to tell at a glance.

fwiw, the haskell page does a great job of this: following the "why use haskell?" gives the classic quicksort example.