Gotta be my Synology NAS. Although the hardware isn’t free. The software is open source.
I moved always from every cloud storage provider to my own private cloud instead! Could not be happier!
My wife loves it too!
Edit: Sorry! Looks like some parts of the Nas is open. Not DSM itself.
My bad I think. Looks like some parts of the Synology Nas is open source but not DSM directly.
https://sourceforge.net/projects/dsgpl/