<i>What I know how to do best is the app store, but I want other type of things that do not require much time investment, but give as good returns as that.<p>What do I do with the money? How do I invest it in making more money quickly?</i><p>Little effort, fast return?  Then you need to take high risks.  Is that really what you want?  Maybe you'd be better off trying to scale your skills (which have gotten you this far) by expanding into other platforms/niches?  Contracting out some of the work could help.