DivestOS is the next best thing to GrapheneOS. The founder, Tad, has contributed a massive amount to privacy on android, I've used it for a few years. It's based on LineageOS and has similar device support..
The two projects are not even remotely comparable. DivestOS can’t ensure security features like memory-isolating the modem, because the range of hardware that it supports doesn't have that functionality. It doesn’t run sandboxed Play Services, so one is limited to generally the apps that are on F-Droid.
They are indeed different projects. GrapheneOS is maximum security possible. DivestOS is best effort security of old/EOL devices to prevent them from being completely e-waste.