– Connie Loizos is a contributor to PE Hub, a Thomson Reuters publication. This article originally appeared here. –

Stewart Butterfield has it made. He’s famous for co-founding the popular photo-sharing service Flickr in 2004. He lives comfortably in Vancouver, having sold Flickr to Yahoo for a reported $35 million in 2005. And investors including Accel Partners and Andreessen Horowitz have thrown $17.2 million behind his two-year-old game company, Tiny Speck, even though the Flash-based multiplayer game it’s been developing, Glitch, hasn’t launched publicly yet.

So why does Butterfield confess to living in “perpetual fear” these days? The truth is Butterfield is under enormous pressure. Expectations for Glitch, which Butterfield describes as a “shared, perpetual game with its own ecology,” are exceedingly high, both because of Butterfield’s personal brand and its ephemeral launch date. (Even after two years of alpha and beta testing by roughly 20,000 gamers, Butterfield declines to disclose when he plans to release the game. “We haven’t finalized (the release date) yet, though the end of September is likely,” he says.)

More significantly, Glitch is hard to categorize. Butterfield credits Zynga — the online gaming company behind the Facebook hits — as “the best thing that could have happened to us, pre-launch. Now there is something like 150 million people who previously didn’t think they’d play a game online and now do.” But Glitch aims to deliver a much higher level of engagement than Cityville or Farmville, two of Zynga’s most popular titles on Facebook. Butterfield says that it’s hard to play Glitch satisfyingly for less than 15 minutes at a time, and that Glitch’s beta testers play an hour on average — with some playing for up to six hours at a time.

At times, what Butterfield seems to be describing is a massively multiplayer online game (MMO) that Facebook gamers can play. The game of Glitch — which involves traveling billions of years back in time in order to re-create the future, by creating and collecting resources, gaining skills, and completing quests in increasingly challenging environments – will invite users to customize their virtual homes or to buy clothing items for their avatars. (Subscribers will receive more customization options, and be able to purchase more a la carte.)