Simple ACPI wakeups manager with some additional options and Unity integration where neccessary. You can select an exact date or relative time to set the alarm and check it's current status. After setting the alarm your machine should wake up on the specified date. In theory it's hardware-dependent but Real Time Clock Alarm (the real name of the feature) was in ACPI Specs since revision 1.0 published back in 1996. One major notice though: some portable devices don't wake up while on battery to prevent accidental damage and battery discharge.
Install wake on plan in ubuntu 12.04
Open the terminal and run the following commands
sudo add-apt-repository ppa:xintx-ua/wakeonplan
sudo apt-get update
sudo apt-get install wakeonplan