You can sell your ebooks through Amazon's Kindle program or Apple's iTunes Connect, which gives you access to a large majority of the digital-book reading market and the barriers for entry are incredibly low. You don't need to invest lots of money to make this happen, but you do need to invest lots of time, not only in writing the ebooks, but in marketing them as well.

Build up a following on your Instagram account and you could quickly be making extra money online. Major brands, gear companies, and even startups are willing to shell out $500-$5,000+ per post to get in front of your audience. While it’s getting harder and harder to build a massive Instagram audience, if you already have a solid niche and are posting quality content regularly with a great camera for taking Instagram photos, with a few small tweaks you can make yourself an influencer. Check out this awesome article from Shopify on how to build and grow your Instagram following to get started.
18. CraigsList – Some things don’t ship very well. Other things may make you feel uncomfortable to sell to someone across the country. Anytime you’re selling a large item or something you just don’t want to ship, Craigslist is a great place to go. It’s simple to list your item (again, take good pictures!). If you don’t like the idea of putting your phone number out there, the interested individual can send you a message to your inbox without even getting your email address.
Now, I know what you’re thinking. Most of the software and apps you use on a regular basis are made by massive companies or established development studios. Well, yes. But many successful apps, particularly those in the Apple and Google stores, are created and marketed by individuals and small businesses. In fact, independent developers made $20 billion in the App Store in 2016 alone.
_{Marketing. When operating as a consultant, you won’t necessarily be marketing your company; you’ll be marketing yourself. You’ll have to “package” yourself in a way that makes people trust you. For instance, if you’re marketing yourself as a financial consultant, ask yourself why someone would trust you with their life savings, and then figure out a way to convey that to potential clients. It might be in the form of a brochure, a portfolio, a sales letter, or all three.}
Understand how a niche website works. A niche website focuses on very targeted, specific information. The content must be specific, useful and interesting to your target audience. Successful niche websites get anywhere from 1,000 to 10,000 visitors per month.[5] You build content on a particular keyword, and you make passive income with Google Adsense or through affiliate links.[6]
So many people dream of writing a book, but never go through with it. Yet no matter what, I’m sure you have experience and value you could give through writing a book. By packaging your skills and knowledge into a downloadable eBook that helps people learn a skill, advance their careers, or start a businesses, you can change someone’s life and even make good money online. You'll just need to employ an easy tool like Sellfy in order to quickly sell PDF files (like an eBook) to your readers.
Get samples. When you first start out as a freelance writer, it can be hard to get work without any published samples. However, it is possible to get quality samples if you are willing to do some writing for free. First, you can publish content on your own blog or website. Also, you can write guest posts for someone else’s blog. Finally, you can write blog posts for free in exchange for a byline.[20]
Like talking to people and helping walk them through problems? You can bring in extra income as a contract customer support superstar for companies all over the world. Due to the 24/7 nature of online businesses, companies are looking for people in different time zones to help deal with issues that their users are having. Better yet, if you have experience in service or retail you’ll be perfectly suited. Check out indeed or the other remote job boards I listed earlier to find opportunities.
Job Boards. When you’re first starting out, you’ll have to go looking for work, and the best place to do that is on one of the online job boards. Places like  Fiverr, Elance, Freelancer, and oDesk are today’s writers’ best friends. They allow individuals and businesses to post projects, and freelancers to bid on them. Take a look around the sites, sign up for the free access in the beginning, and then begin to place bids on the projects that interest you. It will take some trial and error to find your groove, but once you do, the jobs will start to roll in.
Upwork: This website offers a great marketplace for selling just about any professional service. You don't need a merchant account, website of your own or anything else for that matter. All you need to do is be able to provide a high-quality service at a reasonable price. But be informed, you will have to compete with many others that are constantly bidding on open jobs. 
So, where are we supposed to turn to make money the legitimate way online? This isn't just about generating passive income; this is also about finding ways and means to create an active income through the conveniences afforded to us by the internet that will not only help us with our debt obligations, but also empower us to save, invest and get really rich in the future.