Valve, the company in charge of Steam, has discontinued its PC-based streaming box known as Steam Link. The company is selling through its stock, and that will be the end of it.
The Steam Link, which Valve sold for $50, but went as low as $2.50 during certain sales, was an early attempt at what is now a more ubiquitous streaming concept. This device would hook up to your TV via HDMI and accept USB devices such as keyboards, mice, and controllers. Then, presumably with a solid internet connection, you could stream your PC to your Steam Link.
Now, Valve has a Steam Link app, which is currently available on Android phones and Samsung Smart TVs. (Apple rejected the app from iOS devices, due to an issue with purchases.) Steam also supports In-Home streaming, which would allow a user to stream from their gaming PC to a laptop, which could then be connected to a TV.
Steam Link is currently still available in the US, although Valve has stated EU stock is already sold out.