Download the latest version and unzip.
In the ImageJ directory...
On Mac systems the easiest way to get to the ImageJ application folder is to go to Applications in Finder (usually accessible from the Favorites list on the left panel) and right-click the Image J app (e.g. 'Fiji.app') and click 'Show Package Contents'.
Once installed you can access the macros and plugins from the toolsets menu or the normal plugin menu (under 'OSOV'). To add the toolset to the toolbar use the More Tools icon (>>) at the far right of the toolbar (See the ImageJ User Guide - Custom Tools for more information) and select 'OSOV Toolbox'.
If you're getting any sort of 'Not Found' errors when trying to run commands, or if the Plugin > OSOV menu doesn't list a number of items then you may have issue with the version of ImageJ. This version of ImageJ from https://imagej.net/Fiji/Downloads#Life-Line_Fiji_versions will work:
All plugins developed by OpenSourceOV except for the Stack Contrast Adjustment plugin developed by Jan Michalek, Martin Capek, Jiri Janacek.