Mechanical Turk: Amazon's Mechanical Turk is a resource for doing human-intelligence tasks, or as the site commonly refers to them, HITs. You get paid a very small fee for any given HIT and you'll need a good deal of volume to make a substantial amount of money. But it is a resource you can use in your spare time to generate a small income online. 
Drive for Uber or Lyft: If you're in a locale where you can find Uber or Lyft (or even one of the many competitors around the world such as China's Didi), you could easily make a respectable income. The hours are flexible and you can work as you see fit, making it perfect even if you currently have full-time employment but are looking to make some money on the side. 
Join a startup accelerator: Another great option is to apply to a startup accelerator like Y Combinator, 500 startups, or TechStars, where a group of investors will help coach you, connect you with potential partners, and provide startup cash in return for a small stake in your company. The competition is tough to get into these, so don’t rely on them as your only path forward.
You can work as a virtual assistant through dedicated websites, such as Upwork or Zirtual. All kinds of skills are needed, and compensation can vary anywhere between $10 per hour to $100 or more. Obviously, the higher pay will be to people who have more technical skills, such as web building skills and marketing. But you can find work doing administrative tasks at the lower end of the pay scale.
If you have a business, you want to get listed on Yelp! You may not use the software, but some people do, and they use it religiously (and I don’t mean they’ll kill you over it). By listing your business on Yelp!, you’re putting yourself on the map. From here, you also need to start using Yelp! Write reviews of places you go. It’ll be worth it in the long run.
Webinars are quite possibly one of the most potent ways you can make an exorbitant amount of money online. Russell Brunson often says that if you do a webinar every single week for a year, you'll be a millionaire at the end of it. You'll need an audience to train and you'll need to know what you're talking about. Of course, this usually requires having a website and some semblance of an online presence.
Our first overlooked opportunity is selling your knowledge. In this instance, we are talking about creating a course or eBook that you can make available for purchasing online. Because of the automation available today, you may be able to put in the work once when creating your packaged information and then enjoy those checks coming in for months or years to come.