While finding an official "free" license key for has become difficult since Broadcom ended the free version program and the software reached End of General Support years ago, community repositories on GitHub often host collections of keys for legacy and homelab environments. Potential License Key Sources on GitHub
Which of those would you like next?
If you need a powerful hypervisor for older hardware and do not want to deal with licensing headaches, is the industry favorite. Cost: 100% free and open-source. esxi 5.5 license key github