DRS Explorer is created by Daniel C. Roe of RoeBuck Software as described in help menu => about.
It rests on a DOS-prompt program called DRSBuild or DRS Builder Utility possibly by the same author, I'm not sure though.
Edit: DRS Build was created by Stoyan Ratchev, creator of the AI Editor, as described in the download information of the .slp to .bmp converter.