What kind of apps can be built in the crypto ecosystem?

All kind of apps that can be built utilizing the power of fiat currency. Example 1: I can build a blog and start accepting donations in cryptocurrencies - same goes for online games etc.

Example 2: I can utilize the blockchain to proof authenticity of a document, image, sound, will, legal document etc.

Example 3: Filecoin, Siacoin, Storj - P2P file hosting

Example 4: Aragon - Decentralized trust-less companies - Test their alpha version - it seems the solution on the governance of open source apps

Example 5: Decentralized exchanges - check etherdelta.

The above are just really basic examples - we are still in a really premature phase. The whole point of cryptocurrencies is that I can trust and exchange labor, money or whatever with anyone worldwide without me even knowing them.

The worldwide economic crashes were the result of people trusting 3rd parties such as banks, investment firms etc. This problem can be solved.

I think it will be big for virtual gaming assets: https://spellsofgenesis.com/ and https://www.ageofrust.games/

"21" has a framework to assist it and a handful of developers have already built apps:

https://21.co/mkt/

The illegal kinds that have high demand, like darknet markets.