There’s no shortage of project management software available — Microsoft Project is the most high-profile option, but the list of competing startups seems endless. Bellevue, Wash.-based LiquidPlanner is trying to stand out by offering a new approach to the most difficult part of project planning — staying on track when everything goes wrong.

The company’s key innovation is obvious but powerful — deadlines are usually inexact and need to be changed as, inevitably, things don’t go according to plan, so LiquidPlanner doesn’t take a larger project and give each task a specific deadline. Instead, team members list a range of likely completion dates. The service then uses statistical analysis to figure out when a project as a whole will probably finish, and adjusts that estimate as necessary. So if your boss thinks it will take two to four days to finish a task, but you realize it will take closer to two weeks, you can change the range of completion dates, and LiquidPlanner will adjust the estimates for related tasks accordingly.

Naturally, changing schedules mean the project’s plans and goals will need to be revised too, and LiquidPlanner also offers an easy-to-use drag-and-drop interface to make those changes. If a particular task is causing major delays, with just a few clicks a manager can move that task to later in the timeline, or delete it altogether — and again, the estimates for every related task will be adjusted, too.

Co-founder Charles Seybold gave me a demo of LiquidPlanner this morning, and it’s not a one-trick pony — the company has rounded out its key feature with other useful collaboration tools, albeit ones that are less unique.

LiquidPlanner has been in public testing since January, and the commercial version launches today. (Naturally, the company has been using the service to manage its own plans. Seybold showed me a project log revealing how his team quickly spotted problems and scaled back accordingly; despite the hiccups, the company met its launch deadline.) The service is still free for up to three users, as well as for nonprofits; it costs $35 per month for each user above that.

The company is self-financed, mainly by Seybold and his co-founder Jason Carlson. Both of them were managers at Expedia.com. Seybold also worked on Microsoft Project in the ’90s.