Cockatrice, an online and downloadable software program for building and playing Magic: The Gathering for free, was shut down due to a "legal dispute" instigated by Wizards of the Coast.
News was spread via a post about the issue on Reddit. Brukie, the creator of Cockatrice, released a statement on this thread:
"I have received what you might call a C&D letter from Hasbro's lawyers. I say "what you might call" because not only do they want me to shut down, but they also require me to sign a form that basically says I will have to pay a yet unspecified amount of damages. I do believe most of their claims are wrong though. The deadline for sending back this form had already passed when I got the letter in my hands, so I'll have to sort this out with the lawyers first as soon as they're available. I'll keep you posted."