How many Operating Systems can you name ?

The other day when I was trying out Haiku, I had a sudden brain wave. How many operating systems - old or otherwise can I really name? And how many of these have I actually used? To tell you honestly, I could name only a few including the ones I have used. Of course, I lumped all Linux distributions as one entity.

In fact, this is the list of operating systems I could name :
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