This is an evolving version of the script originally developed by Lionel Cons and later maintained for a time by Olaf Bachmann. It now supports many advanced features, such as internationalization and extremely configurable output formats. Development of Texi2HTML moved to the GNU Texinfo repository in 2010, since it was meant to replace the makeinfo implementation in GNU Texinfo.
There was no release of GNU Texinfo with makeinfo based on Texi2HTML, however, because the implementation based on Texi2HTML was abandoned in favor of the current program in GNU Texinfo, which parses the Texinfo input into a tree for processing and supports nearly all the features of Texi2HTML. Latest Texi2HTML sources are thus in the GNU Texinfo repository, although development of Texi2HTML and of the Texi2HTML based makeinfo implementation stopped in 2011.
There are some differences between Texi2HTML and the GNU Texinfo makeinfo/texi2any implementation, even in the Texi2HTML compatibility mode, they are documented in the GNU Texinfo manual. Nevertheless, the route forward for authors is, in most cases, to alter manuals and build processes as necessary to use the new features of the makeinfo/texi2any implementation of GNU Texinfo.
The Texi2HTML maintainers (one of whom is the principal author of the GNU Texinfo implementation) do not intend to make further releases of Texi2HTML. If you have difficulties using the new implementation, you could try to ask on the GNU Texinfo mailing lists.