I know UI Design and a just a little bit of backend. My sideprojects are always more about design and less about technical part, however whatever little technical part it requires, it gives me enough to learn something new.
The way I keep myself motivated to finish sideprojects is that most of the part is right up my alley, design which gives me confidence I can finish it.
For http://typezebra.com/ I learnt a bit of Javascript while for https://bootmystrap.com/ I learnt to design websites properly using LESS CSS.
The way I keep myself motivated to finish sideprojects is that most of the part is right up my alley, design which gives me confidence I can finish it.