If you are using OS X 10.9 (Mavericks) and use Citrix Receiver you might notice, as I did, that my Citrix Receiver sessions would end unexpectedly. App Nap was introduced in the latest release of OS X and enables the OS to save energy by pausing application when they are not visible.
You can turn off App Nap per-app by selecting “Prevent App Nap” on the Citrix Receiver app. I made this change yesterday and I haven’t been disconnected since.
Lewan IT Solutions Technical Blog 