In addition to what daphnissov said:
I don't know of any solution that works like a vCenter or some kind of control panel for multiple ESXi hosts and is compatible with the free version of ESXi. The API limitations make this almost impossible. So if you are looking for some kind of central management for multiple ESXi hosts, you will need to license your hosts first (that was already mentioned).
For licensing, there are several possibilities. For 10 ESXi hosts you will need the vSphere Standard, Enterprise Plus or Platinum licenses and additionally the license for vCenter. Instead of vCenter you might also want to use an alternative, but I can't tell you one here, because I haven't been working with vCenter alternatives before.
The ESXi hosts are licensed once per CPU socket and there are additional support contracts (Support & Subscription / SnS) that can be extended after a certain period of time.
You will find more information here: