VirusTotal

This is an incredibly useful free service that even gives you a limited API. A quick way to verify a download or a suspicious domain before visiting it. You can map out all domains connected to your target domain and even CDN's.

They offer free browser extensions and even a free mobile app. They have a limited Windows Desktop app but this isn't to replace your A/V software. It's more a webmaster tool that can be used by individuals and everyone can contribute in and can vote on if they believe a domain to be malicious or contains malicious content. My favorite part is the VT Graphing feature in conjunction with your API. You can literally map almost everything connected to a domain.

This is an awesome suite of tools for even the home user with a little knowledge or willingness to learn!

Virustotal is an online virus scanner that allows users to check files and URLs for malware. It was launched in 2004 and acquired by Google in 2012. Virustotal offers a comprehensive review of its malware detection capabilities, making it a popular choice among individuals and businesses alike. Its service is free, easy to use, and provides detailed reports on potential threats.
Virustotal operates by analyzing submitted files using more than 70 different antivirus engines, including those from popular vendors such as McAfee, Symantec, and Kaspersky. This approach gives users a well-rounded view of whether a file or URL is malicious or not. Additionally, Virustotal provides other helpful features such as file reputation scores and submission statistics. With the increase of cyber attacks on personal computers and businesses worldwide, having reliable tools like Virustotal can help prevent malware infections and protect sensitive data.

Pretty useful utility website - You can use this website by uploading files, and the website will scan the file into multiple virus scanners. Some antiviruses produce false positives (mostly obscure antiviruses), but if some well-reputable antivirus or more detects the file, that's where you need to think. It has limitations when it comes to filesize, but it isn't that tight. So if you have a download and you're scared about the things it may carry, this is where you need to go.

It also has a URL scanner, which lets you submit a URL, and see if the submitted URL is blacklisted on some security website.