I would like a very deep socket with thin wall that would allow removing/installing a 1/2" copper male adapter (with 3 or 4" of pipe soldered into it) screwed into a drop L buried in the wall. Every such adapter I've seen is a bastard size that no normal deep socket fits well - US or Metric. Some wrenches in a "cowbell" set almost work.
I would also like a tight-space crow's-foot-like wrench to install and remove the spray adapter hose from a Moen kitchen sink faucet while the faucet is installed in the sink and buried up in that special inaccessible space the sink designers came up with.
There's more, but they don't come to mind right now.