General Autocompletion

Does anyone know of a good way to have autocompletion of custom items on a mac? I know this is built into different programs, but what I would like would be independent of the program being used. For example, if I need to type my email address somewhere I would like to be able to enter the first few letters and then have it completed for me.

Basic autocompletion is built into macOS. For example, you can type bjbk@ to get [email protected] or similar.

• Go to System Preferences... (From  Menu or your Dock or Spotlight)
• Go to Keyboard
• Select Text tab
• Click the + button
• Add text to replace, followed by the text you wish to replace it with. The shortcuts work in most applications. (Tested MS Office and others on my system. OS X 10.10.x; Office 2011 v14.5.x)

Alternative to built in text replace:

aText (not free but very inexpensive) on the App Store is a great 3rd party alternative too. Great for code completion or adding dates, times, etc. (I am on no way affiliated with the developer, just a user.)

UPDATE:
Developer's note on the App Store version.

About Mac App Store version.

aText Mac App Store version can no longer fully work on OS X 10.11 El Capitan and later because of new App Sandboxing restrictions. This is not fixable. If you purchased aText on Mac App Store, please switch to non-MAS (non sandboxed) version for free.