www.cowzer.com, and the individual sub-websites within it, are very simply built in order to make it easy for me to maintain. The individual html webpages are formed from smaller blocks of php code in modular fashion, so a lot of common code is reused. I'm pretty good at this and learned a lot from both my own background in IT and also from previous experience with my personal websites.
Dave Gamache For his Skeleton - A dead simple, responsive boilerplate. This gave me the basic responsive frame and is extremely light and simple, making it easy to understand. Absolutely perfect for what I needed. A couple of extra lines of CSS was all I needed to add to get it to my liking. Here are the details and source
CSS MenuMaker For their Menu. I used the basic simple version and it was a bit more complicated to get working as it had a few idiosyncracies which I needed to work through. But then, a responsive menu which can change format when the screen width gets too narrow for a horizontal menu, is not a simple prospect, so a bit of work is to be expected. Here are the details and source
Osvaldas Valutis For his image lightbox, that I use to display photos from thumbnails. It is responsive, which I needed, and behaves very, very, well on small screens. And it looks great too. It needed a bit of easy modification as it conflicted a bit with Skeleton, and I also had to modify some php to build it's command code correctly. Here are the details and source