DR-DOS hasn't been open sourced. Caldera did release the source for the kernel and a few other bits, but the license only allowed free use for evaluation purposes. After 90 days (for a company) or "a reasonable period" for non-commercial entities you were required to buy a license.
Bryan Sparks did open-source CP/M a little while back, but AFAIK he hasn't said anything about DR-DOS so far.
Thats the DR-DOS/OpenDOS Enhancement Project. Its a set of patches for the Caldera OpenDOS 7.01 kernel.
The license file inside the original Caldera OpenDOS 7.01 source archive says:
"Caldera grants you a non-exclusive license to use the Software in
source or binary form free of charge if (a) you are a student,
faculty member or staff member of an educational institution
(K-12, junior college, college or library), a staff member of
a religious organization, or an employee of an organization which
meets Caldera's criteria for a charitable non-profit organization;
or (b) 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."
So that website is incorrect when it says OpenDOS was released under an open-source license. Not surprising though - most websites discussing OpenDOS make this error. Possibly because at the time I believe Caldera did actually talk about open-sourcing DR-DOS, they just failed to to actually follow through.
If he still has the source code, whats needed is for Bryan Sparks to release it under some regular open-source license like Microsoft have done here.
For the actual hardware or PCem, FreeDOS exists and is alive. DR-DOS has also been open sourced.