Ideas for overcooked, dry chocolate cake? Does not need to be served as a true cake . . .

I'd second the trifle/bread pudding ideas. Another option (if you like that kind of thing) is cake truffles.

If I ever have a cake that comes out too dry or some leftover poundcake that is beginning to get stale, I make trifle! When you layer the pieces of cake with a fruit sauce (raspberry or strawberry would be fantastic), some pudding or custard, & some fluffy whipped cream, there is too much wonderful happening for anyone to notice that the cake isn't super tender & moist.

Or make a chocolate trifle

Or maybe a chocolate riff on pan tres leches?

make chocolate bread pudding...they are too good trust me

Individual parfaits ?

Leave the cake in the pan, pour your choice of liqueur over it and allow to soak in thoroughly (it takes awhile). Trader Vic's Kona Coffee liqueur or Kahlúa would be good choices. Curaçao would be another way to go, as would cherry…

Alternatively, brush it generously with some simple syrup: 8 ounces of water to 8 ounces of sugar (1 1/8 cups) brought to a boil, then cooled. The simple syrup will moisten it. Serve the cake warm with some good ice cream. Don't tell anyone - let them tell you how wonderful it is!

Crumble it and dry further in a low oven, then process into crumbs and use to cover a frosted vanilla cake.