Where would
MICROS~1 be if Gary Kildall were to have been litigious? 
  On Fri, 21 Aug 2015,
Jay Jaeger wrote:
  How so?   Digital Research spurned IBM, and would have
had to take IBM
 on as well as Microsoft.  Litigious or not, it would have been a
 seriously uphill battle. 
The influence and basis on, of MS-DOS and CP/M is undenied.
In fact, the clear copyright issue was apparently why IBM chose to ALSO
sell CP/M-86.  However, there are disagreements about whether the pricing
choice was an IBM effort to sabotage the CP/M-86 sales, or a serious error
by DRI.  (I believe the latter)
But, Gary (and Xerox Parc) was not litigious.