It takes less than you think to start. Zero dollars of investment. You can keep your day job. Just two months of nights and weekends. Then launch it. Maybe it’s not perfect yet. But get it out there.

That’s what the guys at Tapbots did. Six months ago they shipped Weightbot, an iPhone app for tracking your weight. It sold 100k copies in its first 100 days. And a newer app, Convertbot, a unit conversion app, is selling at about twice that rate.

Now they’re leaving their day jobs and giving Tapbots 100% of their energy. The plan is to keep things tight though…

Longer term we aren’t looking to get any VC funding, grow to 100s of employees or get bought out by some big corporation. We may get help with support, testing and/or marketing, but development and design is going to just be us two for the foreseeable future. We think that’s the best way to keep the quality of our applications at the level that everyone expects. Our goal is to produce about 4 applications a year. We aren’t going to shovel out crap-ware to cash-in on our names. We aren’t going to write the next Office or Filemaker. We are going to write simple but incredibly polished applications that are created specifically for the iPhone/Touch devices. Two guys, lot’s of passion and a lot of hard work, that’s the Tapbots way.

The Tapbots way sounds like a pretty smart way.