After running a closed beta where pretty much anyone who joined the Steam group was guaranteed an invite, Valve has finally opened up the In-Home Streaming feature to any and all with a Steam account.
For those who may have been living under several rocks since its announcement last year, Steam's In-Home Streaming option will allow users to stream their favourite games across to other devices, providing your network is up to scratch. The system utilises your local network (thus, In-Home) and can offer a gateway to more mobile gaming where your beefy desktop computer can stream some BioShock Infinite to any compatible device.
To gain access to the open beta all you need to do is have a Steam account and opt into the Steam Client Beta
across all devices. For more on what Steam In-Home Streaming is check out the official page