When comparing Rectangle vs Spectacle, the Slant community recommends Rectangle for most people. In the question“What is the best window manager for Mac?” Rectangle is ranked 6th while Spectacle is ranked 7th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Free and open source
Pro Active development
Pro Plenty of window locations you can define
Pro Supports MacOS Mojave and newer
Pro Mouse control
Let's you snap the windows like on Microsoft Windows.
Pro Option to *NOT* show Rectangle's settings in the menu bar
One item less that would otherwise clutter your menu bar.
Pro Free and open source
Spectacle is licensed under MIT with source code available on GitHub.
Pro Simple hotkeys
Spectacle offers easy-to-remember preset hotkeys.
Pro Mouseless
All windows in Spectacle can be controlled with keyboard shortcuts, so no mouse is needed. This makes for a fast way to control windows.
Pro Great UX
Spectacle is easy to use and configure. It's plug and play.
Pro Low footprint
Spectacle only uses up 18-19 MB of RAM, which means there is not much overhead by using this app.
Pro Multi-monitor support
Pro 7+ years of use
Using it for 7 years
Cons
Con Not maintained
The software is free, but no longer seems to be maintained.
Con Impossible to add new functions
While keyboard shortcuts can be changed for the available actions, there is no way to add custom actions which in turn limits the functionality of the app.
Con Limited window sizing capabilities
You can use 1/2 of the screen vertically and horizontally (divide into 4 parts). You can also use the screen in thirds too, but only the left and right third: you can't use the 1/3 in the center. There is no way to do a more granular distribution.
Con Breaks on macOS High Sierra / Chrome or Firefox
Doesn't support side by side windows.
Con Doesn't work with any Adobe products
There are some apps like Adobe Reader that do not work with Spectacle. Basically, any app with a heavily customized UI that breaks OS X accessibility will not work correctly under Spectacle.