I've really enjoyed writing blog posts recently. Not only is it a great way to flex your writing muscles, but writing about a topic, unsurprisingly, helps you understand that topic better too. I've had great conversations with friends about the posts I've written as well.
And sort of in that same vein, I've been developing my own static site generator that I eventually want to move my blog to. It's almost certainly going to be a worse SSG than every alternative, but it'll be mine and that's worth something in itself.
Plus it's just been fun to make! I wrote some gnarly code to generate infinitely nestable layouts that I'm kind of proud of. It's the kind of code that's really cool but you can only code on a project for yourself, because if someone else had to debug it, they might say some pretty unkind things about you.