From the Supertop blog:

We have some news to share. Tiny has purchased a majority stake in Castro. We are still shareholders and will continue working on the app full time.

I would have loved to see Castro and Supertop thrive as an independent gig. On paper, this is good news because it means that the app will be more sustainable thanks to the financial support offered by the new majority stakeholder.

Castro has reached a size where the demands of running the business have been pulling us in too many different directions. We haven’t been able to focus as much on the core work of designing and building a product. Selling to Tiny gets Castro access to more resources, contacts and expertise. By growing the team we can specialize our roles to be more focused individually and get more done collectively. We can get back to what we’re good at and what we love doing.

On the bright side, this might get us the long anticipated iPad version. Who knows, maybe Castro 4 (that is also discussed in the article) will be released as a universal app. I certainly wouldn't mind.