Sometimes when you're working on a new Master in Glyphs, there are too many incompatibilites to turn on "Show Master Compatibility," but you still want to see the other Masters for reference.
Separately, it can be nice to visualize all the Masters overlaid with a slight fill while you're reviewing the family.
Show Other Masters puts this simple functionality close at hand, with the shortcut ⌘` , putting it directly inline with the Master shortcuts (⌘1, ⌘2, ⌘3, etc).
You can download the plugin here: https://github.com/bensyverson/ShowOtherMasters/blob/master/ShowOtherMasters.glyphsReporter.zip
It should be placed in the following folder:
~/Library/Application Support/Glyphs/PlugIns/
You may need to create the "PlugIns" folder.
Enjoy!
Ben Syverson