Let's first look at the most obvious business idea. If you are an expert in the business and you have teaching abilities, then you open a lot of opportunities to apply their knowledge and get paid for it. If you have knowledge demanded by society, that without customers, you do not stay. Learning can be almost anything:
Mathematics, Russian language, physics, etc., which requires pupils and students lagging behind
Using your computer
For this type of business does not require initial investments. All your investment - your knowledge. I remember one article in the newspaper "Exchange + career." One successful businessman asked, "And what will you do if your company suddenly ruined (no matter for what reason) and you will be absolutely no money?" The businessman replied, "I'll take advice. Accumulated money - and reopen his business."