The JAGS-Wiener module by Dominik Wabersich and Joachim Vandekerckhove extends JAGS by adding the distribution “dweiner” for the the first passage time of a drift diffusion process. As far as I know, this is the first third-party JAGS extension that is distributed as a standalone module . You can download the source code from sourceforge, and for Windows users, there is a binary installer.
Dominik and Joachim have documented the process of putting together the JAGS-Wiener module in a tutorial article, which is now submitted to Behavior Research Methods. This article fills a much needed gap in the documentation, and will hopefully encourage others interested in extending JAGS to follow suit.
 There is also the lossDev package for R, distributed via CRAN, which also includes JAGS extensions. This is a little different as it is tied to the R interface.