http://www.iolanguage.com/downloads/

Release 2005 12 05 - Coroutine, true/false/nil, Exceptions/Actors/CLI
implemented in Io
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===============
- Coroutine primtive added
- Exceptions and actors implemented in Io with Coroutine
* new Excpetion API
* Nop removed
* Nil renamed nil and implemented in Io
- true and false added and implemented in Io
* APIs returning boolean values now use true/false
- CLI implemented in Io
- OSX 10.4, bsd and linux build fixes
- add/append fixes for CGI (by Donovan Preston)
- fix for stdint on BSD (by Jer)
- various fixes from Quag
* new Socket binding, simplified, exposed Event object
- unit tests for Socket
- moved to libevent1.1a

NOTE: items with * may cause older code to break