Now, says Spark Capital cofounder and General Partner Bijan Sabet, the firm is starting to turn its attention towards a new target — the rising tide of workplace apps that make work just a little bit more fun.

And Spark had a big victory in this regard just recently: Trello, a beloved work organization app with 19 million users, sold to Aussie software giant Atlassian for $425 million, after raising

Furthermore, Sabet says, the way that business software was historically sold created "natural gatekeepers" — the IT department dictated what hardware and software could be used by employees, meaning that there weren't a lot of ways that even the scrappiest startup could compete.

There wasn't an easy way to try business software before you buy, Sabet says; we may be used to lots of web-based productivity tools having free-to-use services now, but that wasn't always the case.

"You literally had to take a meeting before you could get a trial version," Sabet says.

David vs. Goliath

The thing that changed, Sabet says, is the rise of Apple and the app economy. Suddenly, people were allowed and encouraged to bring iPhones and Android phones to work. And with that latitude came the opportunity for employees to figure out the best tools they need to get stuff done, choosing apps and services "naturally."

This was "liberating," Sabet says, because it meant that suddenly, those "gatekeepers" were listed. Companies could sell straight to their users, not the IT department. If a small team at a company uses Slack, and their coworkers see them, they're going to want to use Slack, too.

It's the same network effect that powers the growth of social networks like Snapchat or Facebook, Sabet says, and now it's starting to hit the workplace, too. And the really great companies, including Spark portfolio companies Trello and Slack, are the ones who are applying a similar relentless focus on the user.

"We're seeing very creative founders," Sabet says. "They can actually innovate here."

Indeed, Sabet says, it's a "red flag" when startups come to Spark with a business model that's a little more old-fashioned, with revenue that comes from selling professional services like setup, installation, and training. The companies that he's most interested in are the ones that can grow in that new, direct-to-user kind of way.

And while Slack and Trello found success by focusing on a broad set of office workers, Sabet says that there's room for other companies, like Mark43 — a Spark-funded tool for law enforcement officers — to find similar success in different industries.

As for fears that companies like Microsoft and Amazon could crush these work-focused startups with their own ever-growing rosters of apps and services, well, Sabet isn't worried.

"We're kind of big on David vs. Goliath here," he says.