it allready launched you can download stam OS or buy alianware alpha and other steam machines

http://www.ign.com/articles/2014/01/07/ces-a-roundup-of-valves-first-steam-machines

Google could do it, and are the most likely to try. Amazon or Facebook might jump in if MS decides to sell Xbox, however unlikely. I don't think the Steam Machine will count as an actual competitive console, but an alternative to one looking to buy a gaming PC, same as the Alienware Alpha.

First of all, Steam OS is only available as a Beta and while anyone can download it, it is not the full version of it. After all, those 300 prototypes they sent one year ago were all equiped with Nvidia GPUs because the Steam OS didn't work with AMD cards at that time. That's something that they'll have to fix for launch.

Secondary, the Steam Controller, meant to be used with the Steam Machines is yet to be launched and we'll only hear more of it (likely the final form and features it will have) during the next GDC in March.

So, because of the two above points it is clear that any PC that sells today under the "Steam Machine" moniker is "only" a regular PC. Wait until we hear about the release date for the "final" version of the Steam OS and the controller, and which specs will have to have those PCs to be able to be called Steam Machines and then how it sells once it launches. Only then we'll be able to say if it wil flop or not.

And by the way, I'm one of those that think it will flop, but until the proper machines are launched it's only my opinion, not a fact.

Amazon. Theyre taking it a little more serious than others and are actually investing in first party.

Apple and Google wouldnt. Not to the hardcore at least.

There is also Nvidia which has already shown interest with making the Nvidia Shield.  If they wanted they could push their hardware with exclusive content, though very doubtful.  But they have made hardware and theyll probably make a shield 2

Apple could literally sell a console to people who don't even play video games...

hmm

It would have to be Google

Apple, Google

But they already have (android/App store), investing in dedicated consoles is financially unrewarding in this day and age for giants who have a much larger market in mobile phones, tablets and other devices.

What about Samsung? They already have their own VR headset! :P

Yeah! I actually want this to spice it up a bit.
I think any of the big companies will definitely make it interesting. - Both for gamers and developers