I upgraded my GCP with a PID kit I bought from a UK vendor that changes the analogue temperature readings to digital along with the 9 bar OPV mod to bring the pressure of the brew head down.
This project goes a lot further and I would love to do it one day.
I've been watching Craigslist prices for Gaggia Classics for over a year just for this. Now if only I had the counter space for the build in addition to my DF64 and Flare 58!
Less fully featured, but more open (Gaggiuino became closed source post people profiting off the OSS).
I'll also pitch another fun OSS project I sponsored a few years back to build an OSS pressure sensor and 0.1g scale: https://github.com/rhit-coultabm/Consistent-Cups-Espresso-Ac...
Since then it looks like Decent has OSS'ed the DecentScale: https://github.com/decentespresso/openscale