Microsoft has opened the source code of GW-BASIC under the MIT license

Microsoft has announced about the release of the source texts of the programming language interpreter GW-BASIC, which was included with the MS-DOS operating system. The code is open is released under the MIT license. It is written in assembly language for 8088 processors and is based on a slice of the original source texts dated February 10, 1983.

The use of the MIT license allows for modifications, distribution, and use of the code in products, but Microsoft will not accept pull requests to the main repository, as the code may only be of historical and educational interest.
The publication of GW-BASIC complements the open-source source texts of the MS-DOS operating system 1.25 and 2.0 from the previous year, in the repository of which even it is observed that certain activity exists.

Source: opennet.ru