Io is a prototype-based programming language inspired by Smalltalk (all values are objects, all messages are dynamic), Self (prototype-based), NewtonScript (differential inheritance), Act1 (actors and futures for concurrency), LISP (code is a runtime inspectable/modifiable tree) and Lua (small, embeddable).

It features BSD license, small vm (~10K semicolons), multi-state (multiple VMs in same process), incremental garbage collector, weak links,
actor-based concurrency, coroutines, 64bit clean C99 implementation, embeddable, exceptions, unicode.

Above from [http://iolanguage.org/]

Remarkable features of Io are its minimal size and openness to using external code resources.[citation needed] Io is executed by a small, portable virtual machine. [https://en.wikipedia.org/wiki/Io_%28programming_language%29]

Like Tcl, TRAC, Rebol, Prolog and Lisp, Io is [homoiconic|https://en.wikipedia.org/wiki/Homoiconicity]. Click [here|https://blogs.oracle.com/blue/entry/homoiconic_languages] for more info on these types of languages.
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