A lot of the Nutanix stuff makes a lot of big claims, which are kind of mostly true...
Nutanix is really mostly just a distributed/scale-out storage platform. Though they only sell/certify it bundled all together with hardware and such, it mostly comes down to the user having a bunch of hosts, each of which has a hypervisor (ESXi, HyperV, and KVM all supported) and some local disk space. Onto each host you put a single Nutanix VM (called the CVM), and pass-through all of the disk in that host to that VM (how the disk is passed through varies somewhat depending on the hypervisor). The CVM then takes that disk and presents it back out as a single pool of shared storage (protocol again depends on which hypervisor it is on). All of the CVMs talk to each other to form a cluster, so that all of the disk from every host server is combined into a single large redundant pool.
There is some more intelligence in it than that - as far as I know the way it keeps VM storage local to the host where the VM is running is unique. It can also keep local copies on every host for shared disks (eg. the master VM in a linked-clone VDI setup), and when combined with a bunch of SSD in each host plus its insanely high RAM requirements that it uses partially for read-cache it is capable of some very high IOPS numbers with very low latency.
We've got a few nodes now at work, evaluating it to host a VDI solution and in the VDI space I think it does show some promise. But over in the general server virtualization side it doesn't fit nearly as well.
And overall I'm still not convinced that "hyperconvergence" is any good. I'm certain I could have built a cluster to run the same VDI workload we have on our Nutanix, but using a more traditional centralized FC storage array with diskless hosts, and done it at the same performance for less money. But then I'm a storage-guy and I'll probably always prefer keeping it separate from the compute.
If you really want to learn lots about Nutanix, here is the site to read:
The Nutanix Bible - StevenPoitras.com StevenPoitras.com