A system which integrates git-hosting with Amazon's Route53 DNS infrastructure.
I've not touched it for a while, but it managed to handle around 20 million queries last month, and at least one DNS-update a day on average.
I need a prettier website, but the technology pretty much just works and hasn't been updated in a long time. I keep meaning to delegate the website-redsigne to my partner.
https://dns-api.com/
In open-source work I've spent the past few weeks restarting my console-mail client, with integrated Lua scripting. The rewrite gives a much more unified API, and a lot better implementation.
Delegating more work to the Lua side of the application makes it more flexible, more customizable, and more interesting to develop for:
https://github.com/lumail/lumail2
Still early work - since you can neither compose a new email, or reply to existing ones, but the core is good for viewing things. (It is a modal email client, with a user-interface that is somewhat like mutt.)