Automating gym bookings
My gym uses an online system to take gym class bookings. People often book way in advance and then cancel on the day. There's no waiting list so if you want to grab a last minute spot, you have to be lucky enough to try and book in when it's free.
Obviously this is tedious to do so I wrote a small script to launch a headless version of Firefox using selenium and try and book me in every 30 seconds.
It's not failed so far :)