2016-01-26: promise 1.0a1 released
Promises are concurrency primitives that let you write asynchronous code in a sequential style. The promise package is a Tcl based implementation of promises modeled for the most part on the Javascript/ECMAScript 6 standard.
Project page and downloads are at http://sourceforge.net/projects/tcl-promise/ .
Reference documentation is at http://tcl-promise.sourceforge.net but it's probably best to start with the posts at http://www.magicsplat.com/blog/tags/promises/ for an introduction.