When comparing NoSleep vs Little Snitch, the Slant community recommends Little Snitch for most people. In the question“What are the best Mac OSX apps for someone that's new to Apple?” Little Snitch is ranked 7th while NoSleep is ranked 26th. The most important reason people chose Little Snitch is:
Little Snitch rules work even at login screen. Even when receiving attempted connection alerts, once logged in LS has stopped and requested permission for them.
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Pros
Pro Lets you close the lid of a laptop
The laptop will not sleep even if you close the lid, but the display will sleep. If your display cannot sleep, simply lower the brightness until it goes dark & turns off.
Pro Protected even at login screen
Little Snitch rules work even at login screen. Even when receiving attempted connection alerts, once logged in LS has stopped and requested permission for them.
Pro Comparatively easy to use
Easier to use than traditional firewall software, but more powerful due to design and workflow.
Pro Protects your privacy
Protects your privacy and helps to prevent unwanted connections.
Cons
Con Discontinued development
Latest release was November 15th, 2014.