If you have an empty room, unused apartment or vacant in-law suite, consider renting it out on Airbnb or another vacation rental site. Tourists will book your accommodations through the site, and you'll pocket a portion of the rental fee. Before you rent, however, make sure you understand any rules or regulations in your municipality, restrictions from your landlord and gaps in your insurance.
With nearly 100,000 different custom extensions both free and paid available in Google Chrome's marketplace, there's a huge opportunity for creating a useful extension for people to use while browsing the web as a low effort business idea. One of my favorite Chrome extensions, Yet Another Mail Merge, which enables you to send bulk customized emails from within Gmail, gives you 50 free credits to send emails and gives you the chance to upgrade to a paid account to unlock more sending—a great upsell for the people who are getting value from the extension. Even free Chrome extensions like SVRF Tabs by SVRF, which replaces your new tab with stunning VR and 360º images, have the potential to bring in new users and eventually drive revenue for the startup's core business. Another fun example from a friend of mine, Kathleen Garvin, is Hide images with NOPE, a Chrome extension that hides images on the web pages you're browsing—to help eliminate distractions and keep you from seeing images (like those of certain politicians) that you may want to hide. This side business idea is particularly great because it also allows you to showcase your development skills—which can be put to work as an adjacent side business idea on a freelance basis alongside the Chrome extensions you launch.
If you don’t mind parading yourself around in public places as a side business idea, and enjoy a little attention, then working as a human billboard can pay a surprising amount of dividends. Renting out your beard, for example can earn you as much as $5 a day while having a brand logo tattooed on your shaven head for five years could pay as much as $7,000—though this type of earning opportunity is admittedly rare. This business idea is definitely not for the faint of heart, and is a little extreme for me, but nonetheless it's been done as a side hustle for many people. You can start by holding a placard or wearing a sandwich board. If you think this is a good side business idea, you can go all the way and turn it into a full on small business idea with enough hard work—plus you won't have to deal with all the issues other more complex businesses have to constantly think about (like reducing churn).
If so, you might want to consider running your own online thrift shop. Whether you focus on fashion especially, another category of product, or prefer to amass collections of interesting items from all over the internet (but especially eBay!), there’s always a strong demand for items with a story. Give your store a compelling, memorable identity, and it will be seen as much more than a simple consignment store.