MSX was a Japanese home computer standard indeed, developed in collaboration with Microsoft, who provided the BASIC ROM implementation. It became very popular in Japan and in a number of European and South American countries. I wasn’t aware that MSX-DOS was also started by Microsoft but I am not surprised. Later versions of the OS were developed by ASCII corporation in Japan.

Fun fact is that the source was released not long ago with restrictions, and there is a newer version developed by an enthusiast called Nextor. Still in use today by many hobbicists.