Cockatrice is a program which simulates games of MTG. Just wondering if we are okay to talk about it on here or not.

Yes, you are allowed to talk about Cockatrice on the forum. However, linking to and providing other users with the means to get Cockatrice is not allowed as the program is in infringement of copyright law. As long as your posts are not about the direct promotion or distribution of the client, you will be fine.

So I guess that would mean I can't make a thread talking about wanting to play on there. Gotcha.

Pretty sure it means you can make a thread about that. But it's just that anyone responding to you should already know what it is beforehand.
So getting new cockatrice users is a lot harder.

Making a MWS/Cockatrice meetup and play thread would be acceptable but linking to materials in which to obtain it would not be.