Can't you just install this type of app to your phone or pc?
For one instance of app, it's possible to install it onto a single machine.
Things get tricky when you want to access the data from multiple devices. Even trickier, when several people want to access it. After a certain point, it's easier to have a "cloud" solution. And since "cloud" is just somebody's else computer, why not make this a computer YOU own?