Wikipedia - Not much, but I did donate to it when I was a poor student. It's not a perfect page but nothing beats it in "Exam procrastination by going in to a deep rabbit hole by clicking hyperlinks on wikipedia".
Sioyek - PDF reader. I was happy to find it when it was still very new, and being among the firsts to donate to it. Pretty wholesome to see many have donated, a bit like seeing your favorite indie-band going big. https://sioyek.info/
Sioyek - PDF reader. I was happy to find it when it was still very new, and being among the firsts to donate to it. Pretty wholesome to see many have donated, a bit like seeing your favorite indie-band going big. https://sioyek.info/