Our apple tree wasn't doing much of anything (it barely even ever flowered), so I finally cut it down and bark grafted 3 different varieties onto it - Liberty, Ashmead, and Cox Orange Pippin. These should all be able to pollinate one another. We also have a Honeycrisp tree nearby that should benefit from this, too.
Super neat! We have a Japanese Cherry Willow, which is a graft. We inherited it with the house and are slowly trying to bring it back to better health. It got pretty unbalanced, but it's already looking better each year. Grafting is such an interesting thing!
Glad it's doing better! Yeah, grafting is nuts. It's crazy that most fruit trees are grafted.