Valve has announced a new, free operating system designed to bring PC games into the living room - and take on Sony and Microsoft at their own game.

Steam OS is being described as the 'Android' of big screen video games, and is available to any manufacturer who wants to make gaming hardware.

Valve, who run the online games outlet Steam (with 50 million customers), and make many exceptionally-rated games including Left 4 Dead, Half-Life and Portal, say the OS is the first of three big announcements it will make this week.

Later this week it is expected to unveil the Steam Box, its own hardware designed to run the new OS.

That could place it in direct competition with Sony's new PS4, the Xbox One from Microsoft and Nintendo's Wii U, as well as the new range of Android-powered gaming consoles.

Meanwhile the new OS was detailed in a press event, with the pitch that it combines "the rock-solid architecture of Linux with a gaming experience built for the big screen".

The BBC quotes an estimate by IHS Screen Digest suggesting Valve's Steam platform is responsible for about 75% of all PC games sold, totally more than $1 billion in revenue in 2012. But with PC sales falling, it knows that to continue to grow it needs to find new and more accessible hardware on which customers can play the more than 2,000 games available on the site.

The new OS includes home streaming, meaning you can play all Windows and Mac games not available on Steam through the OS, as well as options to watch movies and TV, listen to music and share games within your family.

Steam said on its website:

"Hundreds of great games are already running natively on SteamOS. Watch for announcements in the coming weeks about all the AAA titles coming natively to SteamOS in 2014. Access the full Steam catalog of nearly 3000 games and desktop software titles via in-home streaming."