My forks of demos created by others. This is because I see demos that could be done in a simpler, more modern, more efficient way. In some cases, I redo stuff from scratch, with a totally or a at least very different HTML structure (like when seeing form elements done with divs), just trying to get to a similar looking end result. In other cases, I just focus on the CSS, Trying to make it as logical, as DRY and as maintainable as possible, generating as much as I can with looping and mixins. Or I do CSS versions of demos using images that could be generated with code. Or Vanilla JS versions of demos using libraries.