CP/M has been in a sort of legal limbo for quite a while – the code was openly available, but not through a license, but a short paragraph in an email that contained an odd piece of phrasing that wasn’t entirely clear, and could easily be misunderstood as “you can only distribute any derivative works through this one specific website”.
This has now been clarified by the rights holder – DRDOS, Inc. and Bryan Sparks, president of DRDOS… In an email. However, this time the wording is a lot more clear.
“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.”
This still is far from ideal, since a real license, e.g. MIT or BSD or whatever, would be easier, but at least this clears the waters quite a bit.