SafeSleepOnce puts your Mac into safe sleep once and automatically enables normal sleep afterwards.
Safe sleep is also called deep sleep, hibernation or suspend-to-disk, whereas normal sleep is also called standby or suspend-to-RAM.
When SafeSleepOnce is launched, you are asked for confirmation to enter safe sleep. This dialog can be disabled in the preferences.
If you press and hold the Alt or Option key while launching SafeSleepOnce, the preference window will be shown.