CatchCar gives you "a custom menu that consists of only the characters that you use often and add to it. This is different than using Charmap or Keyboard programs that show you the whole character set. Custom menu saves time. See the sample menu on the right that is installed with the program. You need to click on “Edit Menu” to replace with your own favorite characters." By the developer of Whizfolder which I used until the upgrades became too expensive. (They seem to have returned to a more reasonable level now, but I no longer have any use for the application.)
Nor is it restricted to just one character. Even though I use AutoHotKey and Breevy extensively for abbreviations, this might be useful for characters that you don't use often enough to want to learn an abbreviation.