https://github.com/dhewm/dhewm3-sdk

The new SDK hope to create a near mirror of the original SDK to allow modders to port mods to the dhewm3 engine much more easily. This is a vast improvement to the original method of porting mods on a static dhewm3 source. As a result a new mod has already been ported:
https://www.moddb.com/mods/hardqore