Source distribution
Use sidebar on the right to get the latest tarball with the OTPasswd. Currently there're 0.7 release candidates in testing. Plan is to fix any bugs there are, without adding new functionality, in order to create a stable release with all the changes, which were introduced after 0.5 (and there were lot's of those).
Distributions' repositories
Gentoo
With all releases I publish a Gentoo ebuild so installation in this distribution is pretty flawless. I'm working on including it in the sunrise overlay, but it's not currently there. See a bug tracking entry regarding this ebuild.
Debian
There are also works on including OTPasswd in Debian. Here's a bug report.
After 0.7 stabilizes I'll resume trying to put this software in this distros. If you want to help us with any distribution don't hesitate. ;-)