Backup Solutions for Free ESXi
VMware offers a free version of their vSphere Hypervisor with some limitations like the lack of vCenter support. Another limitation is that APIs are read-only, so it's not possible to use the Data Protection API aka. VADP to make Backups.
Creating backups of Virtual Machines is also important on standalone ESXi hosts. The API limitation makes it impossible to create incremental CBT aided backups, but it's not impossible to create full copies of virtual machines. The post explains the technique to create backups and takes a look at solution that use these techniques.