> ICU, the linux kernel, etc.
It seems unlikely that either of these are more widely deployed than SQLite, especially the Linux kernel.
Probably the vast majority of deployments of the Linux kernel include SQLite. Add in all the non-Linux devices (e.g. the billions of iOS and Windows devices) and that's probably far more than the number of Linux installations without SQLite.
I don't know much about ICU, and perhaps you're right that it's one of the most used bits of software. But I can certainly imagine embedded devices that never communicate with users and wouldn't need ICU but do need to store data.
