CaffeinateMe can help by keeping your system running either for a specific time period or indefinitely until you cancel so that you never run into the issue of having your computer go to sleep while downloading a large file or performing a backup. And now, you can also caffeinate individual apps to keep the system active while the app is running.

Version 1.3:

• Caffeinate individual apps
• Minor fixes and enhancements

Requirements

• OS X 10.8 or later