Holochain is a way of building and running applications using just the devices of the users themselves.
In a traditional web app architecture, there is always someone in the middle. You always have a web server. For example, on Facebook, if I want to talk to you, I don’t send a message to you, I send a message to Facebook and then they send it to you. This is now an old story people are familiar with.
Then blockchain came along and said “Ah! We can get rid of the party in the middle… by putting everyone in the middle”. Actually, it wasn’t everyone, but just everyone wealthy enough and tech savvy to be able to be in the middle: the group of miners that hold on to the records. The Blockchain strategy was to come up with one truth at the network level. We’re trying to do something different. Instead of having a bunch of people, outsiders, holding on to the content, it is just us. So if you and I are running a Twitter Holochain, where we each have the program on our device, we don’t need to have anyone else in the middle. It could just be the two or three or ten of us or even the whole world. What is truly radically different is the ability for the individuals to be able to change how they are coordinating or extend what they do without having to get everyone in the space to agree to that change.