Blockchain is a distributed consensus thing.
How do you get bunch of people to agree on something if they do not trust each other?
You use blockchain.
Now days bitcoin is the most popular blockchain it calculates sha crypto hash and those machinses that calculate that use up a lot of power.
So how to make all that number crunching usefull?
Imagine using pifs as an prof of work.
Instead of calculating crypto hash calculate where the informaion is in pi.
Imagine using neural network training for POW.
Also digital curencies are bad because they do not have anonimity. That makes bitcoin a disasster. Since you could have malicious threats like roque regimes(imagine if Nazi’s had it). Or if tomorrow US gets a dictator or if any malicious party with enough reach.