Simple Apple/iOS-oriented app that visually shows you "when" your contacts are. Handy at-a-glance view of how available people (and I guess resources) are across timezones.
Neat site that provides an animated view of the history of a file in git (well, mostly on GitHub and similar forges). Could be handy if ever needing to demonstrate how some code evolved.
Things you're probably not using in Python 3 - but should
Handy little post that details some of the real headline changes that have taken place in "recent" generations of Python 3. I'm happy to say that I make use of a good few of these already.
Extension for Quick Look on macOS that nicely handles all sorts of source code, etc. Especially of interest because it properly renders Markdown documents.