I was lucky enough to be given 2 of those plastic shopping bags nearly full of plums, most of which were on the border of over-ripe. What to do with so many? 2 words. Plum. Butter.
I don't have a recipe for this, it's one of those things you kinda learn by watching reading and experimenting but here's an idea of what you do.
Grab the largest stock pot you own, well in my case I had to, but it still didn't hold all the plums at first.
Turn on burner to medium add a tiny bit of water to keep fruit from burning at first and start piling in the plums, whole or pitted, I decided to do them whole and fish out the pits later. Cook until they begin to break down stirring occasionally and add more if you have them.
Once all are added, reduce heat to medium low, possibly even low, and just cook until the plums have reduced by half. At this point I fished out the pits with my fry spider then pulsed a few times with my stick blender to break up any large skins.
Keep cooking this down until it starts to sheet off a spoon, this is where I add sugar to taste, usually only 1/4 the total mass of total fruit. If I have about 8 cups of fruit mush I'll only add about 2 cups sugar, but this is our taste, we don't like things too sweet. Cook until it gels on a cold plate, you can find directions for this in most canning books and sites, ladle into jars and water bath can at 15 minutes for quarts.
Once our peaches start ripening we'll do the same with them.