Grafting. I like grafting different varieties of fruit trees together to make trees that bear multiple varieties of fruit. So far I've grafted a golden delicious apple onto my crabapple, and a golden orb plum onto my purple plum. It's pretty hit or miss, but cool when the grafts take. I'm going to try grafting some different varieties of stone fruit onto a wild peach tree that I have to see what will happen.
I also like growing fruit trees from seed. I have an avocado tree, an egg fruit tree, a mango, a few red plums, and a firepit peach tree. I also grew some pineapple plants from pineapples that I got from the store, and I got a pineapple from one last year!
I'm not sure why I enjoy it to be honest, other than I just think it's neat to do. I just think the idea of a tree with plums, peaches, nectarines, and cherries all growing from it to be really cool.
I think my favorite is stone fruit so far, since they're fairly different from each other. But it's the one I've had the least luck with so far, too. Hoping it goes well this year!
Sure, here you go. This is where I grafted a yellow orb plum scion (branch) onto my purple plum tree. This is called a bark graft, usually used to graft another variety onto a tree that's getting a little old (like old apple trees). You cut off a large section of the trunk or a branch, then you use a knife to lift up the bark, and you take the end of the scion (with the bark removed from it) and stick it in there. Then you secure with grafting tape. The cambium layers of the scion and tree heal together, and the tree passes nutrients into the scion which grows into a new branch.
There's also YouTube videos showing the various procedures.
I would start with bud grafting, since it's one of the easiest to do. You could get yourself some root stock and bud graft a few varieties onto it and see what happens.