The other type is much bigger and can take months or even years. New features are added from time to time, but must also fit into a well defined architecture.
Both types can be satisfying but require different approaches. The first gives you a bunch of different projects that get shuffled around and easily abandoned. The second requires more discipline as you continually build upon previous layers.
Since they are both side projects, you can go weeks without looking at them or spend all your spare time on them for extended periods.
I have a side project that I have dabbled with for a decade. There are months where I get many features working and others where I barely look at it. It just depends on what else is happening in my life at the moment.