Bryan Sparks, President of DRDOS, clarified the license of CP/M:

Let this paragraph represent a right to use, distribute, modify, enhance, and otherwise make available in a nonexclusive manner CP/M and its derivatives. This right comes from the company, DRDOS, Inc.'s purchase of Digital Research, the company and all assets, dating back to the mid-1990’s. DRDOS, Inc. and I, Bryan Sparks, President of DRDOS, Inc. as its representative, is the owner of CP/M and the successor in interest of Digital Research assets.
Of course, it was "opened" a long time before, but with an unclear clause, mentioning "Unofficial CP/M Web Site" as a licensed place.

The discussion is not over yet, but we believe this statement is equivalent to the well-known BSD or MIT licenses.