Vulnerability Scanning software is a very essential tool for big organizations and companies. However, they also serve an important purpose to small organizations and individuals who do not have the resources to pay for this software. This is why there is free vulnerability scanning software available for everyone to use. Network security is important to everyone. So, here I have a list of the top 10 Free Vulnerability Scanners.
Table of contents
1.Wireshark :

Wireshark is a free open source software and is one of the best free vulnerability scanners. This software is loaded with features like deep inspection, live capture, offline analysis, standard three-pane packet browser, rich VoIP analysis. Decryption support for many protocols, coloring rules that can be applied to the packet list for quick, intuitive analysis. Capture files compressed with gzip can be decompressed on the fly, read/write many different capture file formats, live data can be read from Ethernet, IEEE 802.11, PPP/HDLC, ATM, Bluetooth, USB, Token Ring, Frame Relay, FDDI, and others, etc. Wireshark has the most powerful display filters in the industry. This is a very versatile software in terms of its services on different platforms like Windows, Linux, macOS, Solaris, FreeBSD, NetBSD, and many others.
2.Nmap :

Nmap or Network Mapper prevents security disasters before they happen. Nmap is free open-source software that provides tools for scanning vulnerabilities in your network. One of the most powerful features this software has is its scripting engine. Some other features are: it supports advanced techniques for mapping out networks that are filled with IP filters, firewalls, routers, and other obstacles, it can easily scan hundreds of systems at the same time, most of the operating systems support Nmap. Network Mapper is supported by a big community of developers and users.
3.OpenVAS :

OpenVAS or Open Vulnerability Assessment Scanner is licensed under the General Public License (GNU). It is a free vulnerability scanning software with features like unauthenticated testing, authenticated testing, high level, and low-level internet and industry protocols, and performance tuning for large-scale scans, and a powerful internal programming language to implement any type of vulnerability test. This software is designed specifically for Linux. It is one of the top vulnerability scanners but is not the right tool for inexperienced users.
4.BurpSuite Community Edition :

Burpsuite is a PortSwigger product that is a global leader in the fight against cybercrime. This software is the free version of BurpSuite with limited but powerful features. It has features like manual tools for exploring web security, web vulnerability scanner, scheduled & repeat scans, unlimited scalability, CI integration, advanced manual tools, and essential manual tools. You can proxy your HTTPS traffic, edit and repeat requests, decode data, and more. BurpSuite is available in more than 140 countries. It can report many vulnerabilities, including SQLi, XSS, and the whole OWASP top 10.
5.Qualys Community Edition :

Qualys Cloud Platform powers IT security and compliance cloud apps. This software collects data from 3rd parties cloud platforms and applications for threat intelligence feed. The community edition is the free version of Qualys vulnerability scanner. It has features like instant visibility and unified threat assessment, continuous view of your security and compliance posture, comprehensive coverage and visibility, and automated global IT inventory.
6.Acunetix Vulnerability Scanner :

Acunetix finds vulnerabilities in your website and web APIs. The manual tools Acunetix offers are free for private and commercial use. This software can prevent potential attacks, manage web and network security, automate your scanning, detect SQLi, XSS, and integrate with your SDLC. It has IAST. IAST allows you to find and test hidden inputs.
7.AlienVault USM :

AlienVault USM or AlienVault Unified Security Management provides free IR security tools and a dashboard to help you detect the vulnerabilities in your system and investigate the threats. It provides features like Global Security Gateway. It is web and internet security.
8.SaltStack :

SaltStack helps you control and secure your digital infrastructure. It is a free open source vulnerability scanner but has limited features as compared to its enterprise version. SaltStck provides Flexibility with the best orchestration, Scale i.e. you can control and secure more than 150000 nodes, Action since it is proactive and creates self-healing systems, Security, and Speed.
9.BeyondTrust Vulnerability Management :

This software has IPv6 scanning support for SCAP scans. It can scan your network, web services, databases, containers, virtual environment, and IoT devices as well. In this software, you can avail of features like anti-spam, snit virus, audit trail, compliance management, database security audit, file access control, financial data protection, maintenance scheduling, real-time monitoring, security event log, and vulnerability protection. This software is free for up to 256 devices.
10.Nessus Essentials :

It has the lowest false positive rate with six-sigma accuracy. Nessus Essentials is a free vulnerability scanner but it has its limitations compared to the paid version. It is only available for home network use. More than 30000 organizations use Nessus and it is a well-trusted brand worldwide. It has the deepest and broadest vulnerability coverage. With this software, you can scan up to 16 IPs, advanced support, role-based access control, predictive prioritization, enterprise scalability, configuration assessment, and much more.
Free Vulnerability Scanners are generally the free versions of the paid software where you get only a trial version and if not that then a software with time or features limitation to it.
For reference: https://www.dnsstuff.com/network-vulnerability-scanner
https://www.g2.com/categories/vulnerability-scanner/free