Like others have said, I made these for myself, but they have been useful to other people as well.

Search Wikimedia Commons: canweimage.com (300 - 600 searches a day)

Testing flexbox rules: flexbox.help

Googley Eyes Firefox addon: https://addons.mozilla.org/en-US/firefox/addon/googley-eyes/

Can We Image got included in a listicle on Buffer's blog. flexbox.help started getting use after I posted it as a Show HN and it got picked up by HTML Weekly.