I would like to access "Find My Friends" from the desktop.
Also, is there an API available? I'd like to write code to monitor a person's location over time.
On MacOS 10.10, "Find My Friends" can be accessed by clicking "Details" when viewing a friend in the Messages application.
You can also share screens via "Details" as well, from the desktop Messages app.
I can use the "Find My iPhone" app in iCloud to view the location of my laptop and desktop. Isn't "Find My Friends" basically the same thing except you are getting permission to see their devices. I guess if "a friend" gave you their Apple ID and password, you could use "Find My iPhone" app as a work around.
As of OS X 10.11 "El Capitan", Find My Friends is available as a widget in Notification Center, and in Messages by clicking the "Details" button in the top-right hand corner of an active Messages chat.