They're a breakthrough in Computer Science and enable different use cases for digital payments e.g., machine-to-machine payments. You're trusting mathematics and code and not trusting any entity. Future of cryptocurrencies is a broad topic, hard to answer it here. I'd recommend watching some TED talk on this; Neha Narula has a good one https://www.ted.com/talks/neha_narula_the_future_of_money

Different dapps will have different use cases and need to look at them individually e.g., Graphite built on Blockstack provides a decentralized G-Suite. That provides utility to some users and that utility is very different from an app like Stealthy. There are many problems, ranging from infrastructure issues to UX problems to user education, that need to be solved before we can expect broader adoption of dapps. I'm not familiar with Rinkeby etc so can't really comment. Thanks!

The Stacks blockchain is a separate blockchain. We use Bitcoin for some functionality (for example, miners will need to interact with Bitcoin for burning tokens to participate in our mining algorithm) but over time this might change, see our roadmap for details: https://blockstack.org/roadmap/ One way to think about this is that we're bootstrapping our blockchain by re-using Bitcoin's hash power and may start relying less on it as more miners participate directly on the Stacks blockchain.

It's very hard to say. Our approach is to lower the friction to building/publishing apps and allow as much room for experimentation as possible. We'd rather let real experiments/apps decide what categories end up getting traction. The current list of Signature Fund investments are online here: https://signature.vc

If by "same" you mean as frequently as fiat, I'd say we're probably years if not decades away. There might be other new ways that cryptocurrencies get used e.g., machine-to-machine payments; it's possible that such new ways gain wider adoption first.

It's a new consensus mechanism that tries to combine the best of traditional/classical distributed system algorithms with benefits of proof-of-work. We have Stacks Improvement Proposals (SIPs) for finalizing the details of the consensus algorithm. See this: https://github.com/blockstack/blockstack-core/pull/888

We have over 50 apps listed on Blockstack now: https://app.co/blockstack Our main focus these days is the App Mining program: https://blog.blockstack.org/introducing-app-mining/

I think we're generally in the infrastructure phase (or at best nearing the end of the infrastructure phase). Dapps have a hard time scaling on some of the current platforms and the developer tools are a bit clunky (but getting better). Dapps needs to give similar/better UX and reliability to as the centralized apps. At Blockstack, we've done hardcore R&D work on the core infrastructure and have provided easy-to-use developer tools. We're constantly iterating over our developer tools and helping developers to onboard more users. Giving feedback on those developer tools is probably the most useful thing to us right now.

Thanks for your interest! Blockstack has an open-source community and anyone can join and contribute. I'd recommend that you (a) join our open Slack (link on blockstack.org) and (b) check out opportunities to contribute/learn on GitHub (there are issues that are marked as "help-wanted"). Hope that helps!