Perhaps everyone has heard of bitcoin or cryptocurrencies. They appear in the media at moments when they are drawing their last breath (the price has dropped a bit) or when everyone is going crazy and buying (the price has gone up a bit). However, only a few people are experimenting with using them in their lives. Can something so volatile be used reliably? And if we don't care about the price, can cryptocurrencies be used in other ways? For example, to fund creators, or for crowdfunding. Can you use cryptocurrencies to take out a loan? How to use them in international trade or to promote your products? How to build a local crypto economy in your social bubble? Can bitcoin be used to expand personal and social contacts? We can even use bitcoin as a form of "insurance" against the failure of the traditional financial system.