What Window Management Options exist for OS X?
Spectacle
Open source, available at GitHub, accepting donations
App Store link (will not be updated past version 0.6.9)


Center = Command+Option+C
Fullscreen = Command+Option+F
Left Half = Command+Option+←
Right Half = Command+Option+→
Top Half = Command+Option+↑
Bottom Half = Command+Option+↓
Upper Left Corner = Command+Control+←
Lower Left Corner = Command+Shift+Control+←
Upper Right Corner = Command+Control+→
Lower Right Corner = Command+Shift+Control+→
Left Display = Command+Option+Control+←
Right Display = Command+Option+Control+→
Top Display = Command+Option+Control+↑
Bottom Display = Command+Option+Control+↓
Undo = Command+Option+Z

Per Spectacle' Github:

Spectacle users have recommended Rectangle as an open source
alternative.

Rectangle is maintained as of 2020.
brew cask install rectangle