The CP/M software (and a substantial portion of its source code) was placed into open source in 2001, albeit with a non-standard and somewhat confusing license, stating:
Let this email represent a right to use, distribute, modify, enhance and
otherwise make available in a nonexclusive manner the CP/M technology as
part of the “Unofficial CP/M Web Site” with its maintainers, developers and
community.
The “as part of the ‘Unofficial CP/M Web Site’” portion of this statement has been debated a number of times since. In fact, David Given wrote a CP/M almost-compatible clone, CPMish (previously covered on this forum) for this reason. Because of this confusion, the current holder of the CP/M license, Bryan Chapman, was asked to clarify the license, and he did.
The new license reads:
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.
I’m sure there is still debating to be done, but this appears to be an open license in the vein of the expat or simplified BSD license, allowing essentially all use of the code and binaries of CP/M as provided by Digital Research in the 1970s and 1980s (and after, for that matter).
Many individual machines contain a BIOS that may be copyrighted by some different entity (such as the manufacturer), of course, but as these BIOS routines are typically specific to the hardware on which they run, and free and open BIOS routines are readily available for many CP/M compatible devices and platforms, this is not a big impediment to CP/M everywhere.
Via Mastodon.