In beta and by invitation - but working quite well: Steam In-Home Streaming.
Linux to Linux...Windows to Windows...Windows to Linux and vice versa? Ok, this is seriously cool:
The Linux Action Show did a live demo of it in this episode. Fast forward to the 30:30 mark to skip the earlier show segments if you're not a Linux person.
Or watch via YouTube here:

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Welcome to Steam In-Home Streaming
Steam In-Home Streaming a way for people with good home networks to seamlessly play their Steam games between two computers anywhere in the house.
This feature will be available for early feedback in an upcoming beta test. Beta participants will be randomly selected from members of this group, so join, have fun, and stay tuned for more details!
Linux to Linux...Windows to Windows...Windows to Linux and vice versa? Ok, this is seriously cool:
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Q & A
November 20, 2013 - slouken
Q: Is this like other game streaming services I've heard about?
A: No, you are in complete control over the hardware on both ends and the network between them. There is no data center, no subscription, and it's completely free!
Q: Will this be fast enough for me to enjoy my favorite game?
A: This depends on your hardware, networking configuration and how fast you want it to be. It's free, so try it out and see!
Q: Can I use this to stream games across the Internet?
A: The feature is optimized for home streaming and Internet streaming is currently not supported.
Q: Can someone use my computer while I’m streaming a game from it?
A: No, your computer is dedicated to running the game and input is coming from both the remote client and the local system. It would be very confusing if someone were trying to use the computer at the same time.
Q: How do I get selected to participate in the beta?
A: We will be randomly selecting beta test participants from community members who have joined the Steam In-Home Streaming group
The Linux Action Show did a live demo of it in this episode. Fast forward to the 30:30 mark to skip the earlier show segments if you're not a Linux person.
Or watch via YouTube here:

















