OpenDOS isn't open-source, its source-available. The license reads more like trial software:

"Caldera grants you a non-exclusive license to use the Software in source or binary form free of charge if your use of the Software is for the purpose of evaluating whether to purchase an ongoing license to the Software. The evaluation period for use by or on behalf of a commercial entity is limited to 90 days; evaluation use by others is not subject to this 90 day limit but is still limited to a reasonable period"

The whole opendos thing is pretty questionable, too. CPM is open source as is its' derivatives. Cool so far. But is DR-DOS a derivative of it? Or is it bound by the 'non commercial' license of the 90's which a) was revoked b)isn't exactly open source (limits distribution) in the first place.

Microsofts' releases have the benefit of being unambiguous.