Americans used to gather in front of their TV sets on, say, Thursday at 8 p.m. and tune in to Channel 3. The upside: the whole country had a common cultural bond.

The downside: everyone had to sit down Thursday at 8 p.m.

The requirement for the whole population to watch the same shows simultaneously has evaporated as technology advanced. But what will replace the old system? Will we be able to sign up for just the channels we want? Will we pay for one episode at a time? Will the Internet become the new delivery system?

At this point, the future of TV is still up in the air, if not over the air. But already, all kinds of on-demand variations are available in the form of set-top boxes. (“Set-top” may be an obsolete term. To balance one of these boxes on top of today’s flat screens, you’d have to be in Cirque du Soleil.)

This week alone, there’s both a new Apple TV box and a new Roku box in three flavors (HD, XD and XD/S). Each is inexpensive, each is half-finished  but each could be the gateway to a disruptive new future of à la carte TV.