Online poker. Many people make very nice profits (50-100k+/yr) just by playing low to mid stakes poker 4-6 hours a day.
It takes a lot of hard work, study, and hours of experience to become a winning player. It's not something I'd recommend to the highly risk averse if you plan to make a full time job of it, however; it can be very rewarding in a monetary and non-monetary sense, i.e. spend more time at home, you're your own boss, set your own hours, etc.
Like any job it also has its drawbacks. Poker is a lonely profession and it can be easy to pick up bad habits like not eating well, not exercising, and gambling (prop bets, sports betting, blackjack, etc.),
As with any self-employment/investment venture, you must be highly disciplined and learn things like bankroll management, setting a stop-loss, being honest with yourself and forcing yourself to analyze your play with hand tracking programs, and controlling "tilt" (not letting emotions cloud your judgement and logic).
PM me if you want to learn more.