Just discovered the service called “ownCloud”. It seems to be a non-proprietary equivalent to DropBox, available to anyone who is leasing their own space on an internet-connected server. It has recently been rebuilt (or if you prefer gobble-speak) re-architected; and no longer depends upon PHP. I guess this means that anyone who currently installs the most up-to-date version is participating in a beta-trial (like taking the Covid-19 vaccination, maybe?)