I used to have a very stable internet connection, but since moving flats my IP was changing on a regular basis when my router kept crashing.
I use Amazon Route 53 as my DNS for most of my domains and while there's plenty of decent tooling for keeping DNS entries up to date if you use DynDNS or NoIP there wasn't anything that worked for keeping Route 53 entries up to date. So I just made my own.
This is just a very small and quickly hacked together bit of python using the Boto 3 AWS SDK which I run in a cron job on my home server and it seems to work fairly well.