I have come up with 3 ideas in the past that worked out well for me. I wrote a popular MP3 search engine pre-Napster, a site dedicated to price tracking in the

I have come up with 3 ideas in the past that worked out well for me. I wrote a popular MP3 search engine pre-Napster, a site dedicated to price tracking in the game EverQuest, and even a technical analysis website for predicting price movement in Exchange Traded Funds (ETFs). Each one of these worked out well enough to live off at the time. The first two of those projects worked just because the underlying "thing" was huge at the time (MP3s, EverQuest). That last one required actual marketing, buying ads in magazines related to the field ("Technical Analysis of Stocks and Commodities", etc). But I knew the audience for the ETF idea likely had a lot more disposable income, so the monthly charge was high. Unfortunately, as I've gotten older and have a "real" job, I no longer have that desire to write more code after work, so these sorts of ideas and projects have stalled out. The point being if you can find a niche that's popular, or even something you are just very interested in (in my case, at the time, technical analysis), you can likely make money off of it as a software engineer.