DMDX closed source, windows only, text-based stimulus file, millisecond-precise
PXLAB open source, java based, for on- and offline use, seems to measure very precisely using System.nanoTime(), as document on the website. Has its own, text-based stimulus description. However, looks like not developed further because the main (and sole?) developer, Hans Irtel, died in 2008.
WEBEXP open source, java based, includes server, new xml-based format for stimuli, uses System.currentTimeMillis() instead of System.nanoTime(), and may thus be less precise than PXLAB
AFFECT closed source, windows only, graphical interface. does not allow direct editing of the script in text format?
FLXLAB C++ for windows and mac, open source
PEBL C++ for windows and linux, open source, has its own text format
It is a big mess that all these projects use totally incompatible stimulus files. Furthermore, I believe it is a dead end to keep developing these new formats that all end up being miniature crippled programming languages. Why not use an easy-to-learn language and make it accessible for the programmers? That is what worked perfectly for social psychologists who program their eperiments in authorware. Authorware was easy enough for your typical psychology phd student, and a lot of material was available to be re-used. Unfortunately, it is not being developed further.