The current release is : SimpleTest v1.1alpha.
By the way, don't be scared away by the
alpha tag :
quite a few users actually use SimpleTest straight from SVN.
If eclipse is your IDE / editor of choice, you might consider the Eclipse plugin.
For automatic "find and install", the URL is :
SimpleTest has been packaged by the community to different flavours.
Note : careful, some versions are not always up-to-date.
The source code is hosted on Sourceforge as well : you can browse the SVN repository there.