Extempore supports interactive programming in a REPL style, compiling and binding code just-in-time. Although Extempore has its roots in ‘live coding’ of audiovisual media art, it is suitable for any task domain where dynamic run-time modifiability and good numerical performance are required. Extempore also has strong timing and concurrency semantics, which are helpful when working in problem spaces where timing is important (such as audio and video).

Some useful links:

Main project page
http://extempore.moso.com.au

Extempore source code
https://github.com/digego/extempore

Documentation
http://benswift.me/extempore-docs/

Mailing list
https://groups.google.com/group/extemporelang