Ah, video arcades.
Video arcades work on a very specific principle: connectivity. In an arcade, you can play video games. You can even play video games with or against a small number of people (generally the games are either two or four player). That's connectivity, sure. But the real connectivity swirls around that.
There's asynchronous play - a high score table is the obvious example. You play with people (against people) without them even being there. The "line" is another example of connectivity: a dozen people crowded around the Street Fighter cabinet, lining up to fight the winner. While not playing - it happens a lot either because you're out of cash, not feeling that interested, or in a line - socializing is common. An arcade works on the principle of connecting you to other people while giving you an excuse: video games.
In America, the arcade went out of style in the eighties with the advent of home systems. The idea was that your children could come home and play games with their friends or family, instead of running off to the arcade to spend money with strangers far away from mommy's watchful eye. The crash of the home video game caused a revival in arcades for tolerably obvious reasons. Then the arcades crashed again as consoles revived...
In Japan, arcades remain popular even today, presumably because Japanese culture isn't really conducive to chummy family life. Legend has it that Space Invaders was so popular it caused a shortage of 100 yen coins, and even today weird new Japan-only arcade games are developed basically every year.
The arcade never died even in places where it seemed to. It simply mutated. There is always going to be a need for a place to connect while occasionally playing video games. In many places, the internet cafe has taken the spot that the arcade used to inhabit. Fundamentally, they're the same beast, except that the internet cafe uses computers that can play many games (and serve many purposes) instead of getting stuck with aging arcade cabinets. They also have a different atmosphere, of course.
Another example you might not guess is massively multiplayer games such as WoW. Fundamentally, these are games which use the exact same basic principles as arcades. You (and maybe a small group of friends) play games, often to compete asynchronously with others for status (rare equipment, level, rank...)
And, ask anyone, a MMOG is all about waiting. You'd think that a game you're running on your computer would let you play all the time, but that's not the case: you wait for travel, for spawns, for friends, for bids, for hundreds of things.
I bet if you compare play-to-wait times, you'll find that an MMOG has almost the exact same ratio as a popular arcade. And almost the same player reactions: some players will socialize, others will play secondary games, others will watch...
So, yes, fundamentally a MMOG is simply an arcade.
Can you think of anything else?
How about new cell phones?
Yeah, cell phones are fundamentally about chatting with your friends - frequently asynchronously using texting. But chances are, if you are the sort of person who texts, you also play with your phone. Not just games: music, photos, web surfing, all of these serve the same basic purpose as games, and are "asynchronous" in that you can share the results with people after you finish, rather than having to have them around while you do it. "Hey, look at this cool pic..."
Cell phones are evolving into arcades. Or, at least, a weird partial dispersed arcade...
I don't think it'll be long before phones evolve to fill this niche more perfectly. I can't predict exactly how this will happen, but I think it'll largely revolve around easier interfaces. Maybe cell phones that have touchscreens a'la the DS?
Can you think of anything else that is an arcade? Or maybe you have some thoughts on the future of cell phones?