This is so rude from Zendesk. In case you think someone has ripped of your product, in any way, you (as the CEO of a 30+ company with 10,000 customers) SHOULD NEVER, EVER write something like that.
I'm 100% with Freshdesk on this one specifically because of the tone of Zendesk and Freshdesk. The way Mikkel responded to Freshdesk is silly and childish.
If someone were to make a knock off of my product, I wouldn't tweet at them like Mikkel did. Or support one of my buddies (who is perhaps disguised as a blogger for blog XYZ) that's trolling a company's image, saying that they're the same as Zendesk. Or calling them Indian cowboys.
Zendesk, I hope you understand that you've turned me (an actual person who supports everything you do, and someone who talks to the folks at Assistly with a great and friendly tone) into someone who honestly hopes you loose this "battle" and have left a nasty look in a lot of people's eyes.
I don't know much about Freshdesk's product, but I know the way they reacted was nice and professional (exactly the opposite of how you responded). +1 on that.
Lesson learned: You don't do marketing by bashing on someone's product without looking like an ass (and perhaps loosing a couple customers).
P.S.: (to the Freshdesk folks) Congrats on stepping up and putting time in to create a page like this. I would have maybe included screenshots of the product to further help your customers understand that you're not a knock off of Zendesk.