List of free virtual-machine stuff for developerππ½
If you're looking for all programming tools around virtual-machine (not just free). Check this page List of virtual-machine Programming Tools
KVM
KVM (for Kernel-based Virtual Machine) is a full virtualization solution for Linux on x86 hardware containing virtualization extensions (Intel VT or AMD-V).
Tag: virtual-machine

VirtualBox
VirtualBox is a powerful x86 and AMD64/Intel64 virtualization product for enterprise as well as home use.
Tag: virtual-machine
Virtual Machine

Virtual Machines Azure
Build Linux and Windows virtual machines (VMs) and save up to 80 percent with Azure Reserved Virtual Machine Instances and Azure Hybrid Benefit for Windows Server.
Tag: virtual-machine, azure, hosting-dynamic
1 Year free: 750 hours B1s burstable virtual machines/month
Vagrant
Vagrant is a tool for building and managing virtual machine environments in a single workflow.
Tag: virtual-machine
Open Source

OSBoxes - Virtual Machines
Homepage of site that offers virtual machines (VDI & VMDK & VHD) for VirtualBox and VMware. Run VMs inside VirtualBox and VMware on any host.
Tag: virtual-machine

BSD Hypervisor
A hypervisor/virtual machine manager available on FreeBSD and Illumos.
Tag: virtual-machine

XCP-ng - XenServer Based, Community Powered
Based on XenServer, XCP-ng is the result of massive cooperation between individuals and companies, to deliver a product without limits.
Tag: virtual-machine
Virtual Machine Manager Home
The virt-manager application is a desktop user interface for managing virtual machines through libvirt. It primarily targets KVM VMs, but also manages Xen and LXC (linux containers).
Tag: virtual-machine