Ksplice (Oracle) was first, followed by kgraft (Suse), and kpatch (RedHat).
According to the article below, kpatch is x86/64 only, uses ftrace, provides runtime patches only until the next minor kernel release on a standard license, does not address all CVEs, and cannot be used with "SystemTop or kprobe."
"KernelCare has no such limitations."
https://blog.kernelcare.com/competitors/kpatch-overview-of-e...
Ksplice was done by MIT students, not Oracle. I used it long before Oracle bought it, initially with my own patches (and actually after that as a "legacy" customer). kpatch isn't just x86_64; it's in at least ppc64le RHEL 7, although not for the "alt kernel" on the POWER9 systems I use.
I don't know whether it's the case, but their comparison rather suggests Kernelcare is based on Ksplice.
Kernelcare has given me 48 hotfixes on a 3.10 kernel that I booted last year.