Starting in 1999, Randy started looking for ways of using Build-like features to enhance ZDoom and outgrow some of the limitations enforced by the use of a BSP algorithm. These forays didn't pan out entirely, as ZDoom still uses a BSP tree, but some elements (such as slopes, cameras, skyboxes and stacked sectors) were implemented as a result. Other traces of Build support can be seen in the CustomSprite actor and a limited ability to load Build maps.
But it also resulted in a ZDoom-based Duke Nukem 3D source port, entitled ZDuke. ZDuke had one release, based on ZDoom 2.0.48, and was afterwards more or less abandoned. In November 2009, after some people expressed interest in this erstwhile project, Randy uploaded the ZDuke source code to the ZDoom SVN ( ). The thread with this discussion and the announcement of the release was in the "off topic" forum and therefore unfortunately pruned out. However, it mentioned that the ZDuke code is outdated and unsupported.
Note that merging ZDoom and ZDuke (even an updated version) is considered more trouble than it would be worth. The internal game logics are too different to be conciliated in a single engine in a streamlined and stable fashion.