This startup took a famous Toyota management method and put it in an app

Trello, a super-popular free app that helps organize projects for individuals, teams, and companies, announced that it's hit 10 million users.

To keep that train going, Trello is also launching an enhanced, paid version of Trello for businesses as it hits the gas pedal on its ambitions to hit 100 million.

Trello's whole approach is taken from the kanban project management method, which traces its roots to Toyota industrial engineer Taiichi Ohno in the late 1940's. Basically, you use post-its on a whiteboard to indicate the status of individual parts of a project.

For so-called "lean" programming teams, kanban is a handy way of keeping track of who owns what. By breaking software development into discrete chunks, it's a visual way of checking who's responsible for what, and how far along it is.

In 2011, Trello spun out from the 15-year-old Fog Creek Software - which also spawned the popular Stack Exchange online programmer hangout.

The project got its start when the Fog Creek team noticed that lots of the developers they met had kanban whiteboards in every meeting room.

It was originally code-named "Trellis," the architectural term for a structure that supports plants - as in, it'll support you as you grow. But a few weeks ahead of the original launch, they couldn't get the Trellis.com domain, and so came up with "Trello" at the last second. A startup was born.

Trello has made its mission to take the kanban methodology and put it into an app that makes it more broadly applicable outside of Toyota production lines and developer startups, in much the same way that well-funded unicorn Slack made developer chat tools more accessible to the workplace.

"We've tried like 15 things over the years," says Trello CEO Michael Pryor, who also co-founded Fog Creek and sits on Stack Exchange's board. "Some of them have been successes, some have been flops."

Today, Trello has some big customers like University of California Davis and Expedia, plus it's considered by many users to be an essential work and life organization tool, right alongside popular apps like Evernote. Pryor even says people use Trello to plan birthday parties and weddings.

Trello's app and website takes the Post-It concept of kanban and takes it to the next level, with data like Salesforce leads and GitHub pull requests integrated straight into Trello's "cards," plus all kinds of alerts, reminders, notifications, and team features to keep everybody on the same page.

With the new Business Class edition of Trello, Pryor says, you get enhanced integration with other services, including Box, Salesforce, and Slack. Plus, priority support when something goes wrong, and enhanced permissions so not everybody in a big company can see data they're not supposed to.

The real challenge for Trello in search of those 100 million users, Pryor says, is making sure it keeps a solid focus on making the product usable by everyone, not just developers. For example, its programmer users keep asking for features like dependencies, where one Trello card can't resolve until another one is moved up the stack.

"That's not the kind of thing we're planning," Pryor says.

But by keeping a broad focus on making organization accessible to everyone, Pryor thinks that Trello can keep growing - and that while it took Trello from 2011 to 2014 to get to four million users, it'll only be a year before it goes from 10 million to 20 million.