[jfk13]

My guess (not having tried any of these three!) is that the best chance of achieving some kind of income would be the SaaS product, assuming you really can find a niche issue and provide (and market) a solution to it.

For an ebook on a technical topic: it may be pretty difficult to write something so compelling that enough people will be willing to pay money for it. You'll be competing against what people can find free with Google, on stackexchange, etc.

And mobile or web games: there are so many of them out there, do you really think you can stand out from the crowd? I bet the proportion that actually make a worthwhile amount of money is pretty small.