I'm not sure if they are considered startups per say, but I've started two profitable companies while working a day job (to the point where I could quit my day job!) http://www.AUsedCar.com and http://www.BudgetSimple.com . I should say I also created a failed startup during that time. The biggest difference between the successes and the failure were that the successes did not require me to answer phone calls, make sales etc... In other words, completely passive income businesses are the easiest to do with a day job.