Steam today released a beta client that has one very interesting and useful feature 'Remote Downloads'.
The remote download feature allows users to log into their steam account via the steam website on any pc or phone and initiate downloads on your home PC or MAC. For this to function your home system needs to be on and the steam client running.
The steps to use the feature once you have downloaded the beta client are as follows:
1. Log into your Steam account online from your computer or mobile device at www.steampowered.com
2. Visit your Games list by navigating to the Community and then clicking GAMES in the secondary navigation bar. If you’re logged into the Steam client, the games list will reflect the installation state of your library on that machine.
3. Locate your game and tap the install button to initiate your remote download.
Steam appear to be having some issues at the current time and you may not be able to use the remote download feature straight away, as it is still a beta this is expected.