Which popular apps prevent sleep on Mac OS X?

Question

The main reason a Mac won't go to sleep is because of a 3rd party app. If there was a list of popular apps that have been known to cause sleep issues, it would make debugging this issue easier.

Which popular 3rd party apps are known to cause sleep issues?

Answer 1

Known to cause sleep issues:

• Better Touch Tool: Even when it is disabled, as long as it's running, sleep mode won't work.
• Stack Exchange Notifier: more info here.
• Symantec Encryption Desktop: more info here, Symantec's Official Reason here.
• NoSleep: App that does what it says. Although this is the main purpose of the app, for troubleshooting purposes it's good to check whether it's installed and accidentally on ;-)

Could potentially cause issues:

• Dropbox caused problems in Snow Leopard.
• Spotlight can prevent sleep, especially if you just installed Mac OS X.

Apps that have never caused sleep issues:

Answer 2

from http://support.apple.com/kb/HT1776 (Why your Mac might not sleep or stay in sleep mode from apple support) Open applications can affect sleep

Software that accesses the hard drive will delay sleep mode until it is either quit or done accessing the drive. For example:

• Songs playing in iTunes.
• A movie disc playing in DVD Player.

How can I determine what is causing a sleep issue and how can I resolve it?

These are the most likely causes and solutions for sleep issues:

• Sharing preferences: Enabling sharing for any connections can potentially disable sleep. Turn off file sharing if it's not being used.
• Bluetooth settings: Bluetooth can wake your computer if you set the "Allow Bluetooth devices to wake this computer" checkbox in Bluetooth System Preferences.
• Are a keyboard and mouse connected and working correctly?
• Do you have any other external USB or FireWire devices connected? Try removing or disconnecting them one by one, when not in use, taking care to dismount any that are storage devices before disconnecting them.
• Do you have a print job in the Printer Queue? Remove any print jobs that are in the queue.
• Is Spotlight indexing? This can take anywhere from several minutes to several hours after a new installation, or after connecting a storage device which contains unindexed data. Indexing prevents idle sleep.
• Additional Software: Try a Safe Boot to help isolate a software issue.
• Put your ear near your computer. Do you hear the "clicking" sounds of hard disk access?
• Energy Saver settings: If the computer and display sleep timers are set to "Never", the computer will not sleep.

Answer 3

Spotify could be one

pid 390(coreaudiod): [0x00018a5f0001175d] 00:02:05 PreventUserIdleSystemSleep named: 
"com.apple.audio.context442.preventuseridlesleep" 

Relevant Spotify community thread

Answer 4

Open Activity Monitor and it can tell you

Answer 5

Also, the Apple Support Article "Why your Mac might not sleep or stay in sleep mode" is a must read when trying to resolve sleep issues.