This is not depression, at least not as clinically defined. It just seems as though you are lacking motivation. My best advice to you would be to continue work

This is not depression, at least not as clinically defined. It just seems as though you are lacking motivation. My best advice to you would be to continue working on your own info product or start a new one or some other software project, something you can be excited about. Your investment in it should be enough to keep you motivated whereas working for another company (at this point, based on things you've said) would mean that your only motivation is in collecting a paycheck--which will lead you to true depression.