GrbZDoom was a fork of ZDoom created and maintained by Grubber. It became the basis to the ZDoom Community Build. After the release of the Community Build, Grubber released a few more builds of ZDoom variants, updating to the ZDoom 2.0.98 and then 2.0.99 codebases, but they kept the Community Build's convention of just being named ZDoom and appending a 'x' suffix to the version number.
.99x got three updates, the last version being released on May 7, 2006. It then corresponded with ZDoom SVN r83. This was also the last build of Grubber's releases.