I started BuySellAds (http://buysellads.com http://buysellads.com) while employed full-time at HubSpot (http://hubspot.com http://hubspot.com). A few years afte

I started BuySellAds (http://buysellads.com http://buysellads.com) while employed full-time at HubSpot (http://hubspot.com http://hubspot.com). A few years after leaving, my company ended up on the Inc 500 (http://www.inc.com/profile/buysellads http://www.inc.com/profile/buysellads) and we're still doing quite well. - I had the project specifically spelled out in my employment agreement with them since I had already been working on it for a while. I started working for them because I genuinely believed in their mission, and there was a certain allure of a steady paycheck after freelancing for a while. I made the decision to leave after about a year of trying to juggle both. - By the time I left HubSpot was 50 people and they had plenty of funding, so while perhaps they would have liked for me to stick around, there's nothing I did that has ultimately contributed to them becoming the billion dollar company they are today (a nice humbling lesson for the youngster I was back then...). - I actually think doing this (as long as you can keep it clean legally and actually own what you're building in your spare time) far outweighs quitting your job before starting a company. I wrote a post on Quora about this in a little more detail (http://www.quora.com/I-plan-to-quit-my-job-at-a-software-company-and-do-my-own-startup-Im-24-single-with-2-5-years-of-savings-195K-with-no-debt-health-issues-How-much-of-my-savings-should-I-invest-in-my-own-startup/answer/Todd-Garland?__snids__=486789676&__nsrc__=1 http://www.quora.com/I-plan-to-quit-my-job-at-a-software-com...)