The official website: http://www.omnigroup.com/omnifocus
Available on Mac and iOS
Some interesting Resources Covering Catch:
1. http://www.usingomnifocus.com/resources/ An In-depth site covering a lot of how to use Omnifocus
2. http://www.omnigroup.com/blog/category/OmniFocus Omnifocus' Official Blog
This is a running list! If you have any sources you'd like to add, please share it below and I will add it to the list!
NB: I don't own a single Apple product(well except the kinds you eat and juice) so I haven't played around with this.