Kali Linux - https://www.kali.org/downloads/
Kali on Windows - https://www.kali.org/docs/wsl/win-kex/
Flare VM by FireEye - https://www.fireeye.com/blog/threat-research/2017/07/flare-vm-the-windows-malware.html
Commando VM by FireEye - https://www.fireeye.com/blog/threat-research/2019/03/commando-vm-windows-offensive-distribution.html
TraceLabs OSINT VM - https://www.tracelabs.org/trace-labs-osint-vm/
Parrot OS - https://parrotlinux.org/download.php
Black Arch Linux - https://blackarch.org/downloads.html#ova-download
TAILs Linux - https://tails.boum.org/
CSI Linux - https://csilinux.com/
SIFT Workstation - https://digital-forensics.sans.org/community/downloads
REMnux - https://remnux.org/
Buscador VM - https://inteltechniques.com/buscador/
WhoNix - https://www.whonix.org/
TAILS - https://tails.boum.org/index.en.html
Qubes - https://www.qubes-os.org/
QEMU - https://www.qemu.org/
OpenBSD - https://www.freebsd.org/
Virtual Box - https://www.virtualbox.org/
Virtual Machines from Microsoft - https://developer.microsoft.com/en-us/microsoft-edge/tools/vms/
Docker - https://www.docker.com/
Autopsy Sleuth Kit (Forensics) - https://www.sleuthkit.org/autopsy/
Access Data FTK Imager (Forensics) - https://accessdata.com/product-download/ftk-imager-version-4-3-0
Termux Android Terminal Emulator - https://termux.com/
ProxMox - https://proxmox.com/en/
pfSense (free FireWall) - https://www.pfsense.org/
ClamAV (free Anti-Virus) - https://www.clamav.net/
TCPdump (free packet analyser) - https://www.tcpdump.org/
Snort (free intrusion detection system) - https://www.snort.org/
Security Onion (free log management and monitoring) - https://securityonion.net/
How to setup a Virtual Lab - https://leanpub.com/avatar
Setting up a Malware RE lab - https://labs.sentinelone.com/building-a-custom-malware-analysis-lab-environment/