ESXi 5.5 (and all newer versions) comes with a 60-day full-feature evaluation . This is usually enough for temporary testing or data recovery tasks. Conclusion
Several users maintain lists of "bonus" or "working" license keys for legacy VMware products. These are often used by home lab enthusiasts to keep older hardware running. Curated License Collections : Repositories like VMware-ESXi-License-Keys by hegdepavankumar esxi 5.5 license key github
If you are using GitHub to find resources for your ESXi 5.5 setup, pivot your search away from illegal license keys and toward helpful community tools: ESXi 5