spectacle

Spectacle is a free Mac application that lets you move and resize windows on your screen using keyboard shortcuts, without ever touching your mouse. You press a key combination and the window snaps into place: left half of the screen, right half, a corner, the center, or fully maximized. That covers the most common layouts people set up by hand every day.

Beyond simple halves, Spectacle can divide the screen into thirds. Press the same shortcut twice and a window shifts between one-third and two-thirds of its region. You can also step a window through the three horizontal columns one press at a time. If you have more than one monitor, there are shortcuts to send a window to the next or previous display without touching the mouse.

If you move something by accident, Spectacle keeps a history of window positions so you can undo and redo individual moves. The keyboard shortcuts all have defaults out of the box, and every one of them can be changed or turned off entirely in the app preferences.

A few limitations are worth knowing. Spectacle works through the Mac accessibility system, which most standard applications support, but some apps build their windows in non-standard ways and cannot be moved or resized by Spectacle at all. Terminal apps like iTerm 2 impose their own sizing rules so that text rows and columns stay whole, which means Spectacle has to try several times to fit those windows and the result can look slightly jumpy.

The project is no longer actively maintained. The author kept it available as a download and left the source code open, but no new fixes or features are coming. The README points to Rectangle as a community-recommended open-source alternative that covers the same use case and is still under active development.