Official (stable) builds
Official stable builds of PONScripter can be found on the Releases page of Uncle Mion's ONScripter Corner.
Note that "stable" is sort of a relative term with PONScripter. Its development thus far has been focused on making it work with the English translation of Narcissu 2; there are some areas where it's way behind ONScripter-EN. Now that the Narcissu 2 translation has been released, PONScripter development will focus more on bringing it up to date with ONScripter-EN.
Unstable "nightly" builds
We now use a semi-automated build system for PONScripter called ONSBuild. When we invoke ONSBuild, it grabs the latest version of the code from the Subversion repository, builds it for OS X and Linux, and uploads the resulting builds to my web server. If you want to try the latest and greatest version and there's no official release, you can check the ONSBuild output directory to see if there's a build there. Details about each build can usually be found in the CHANGES file.
ONSBuild only makes Mac OS X and Linux (both i386 and x86_64) builds; I don't have it set up to do Windows at the moment.