If one needs to create an nfs server to test esxi, all one needs is a linux nfs server.
Some people prefer freenas or openfiler, others simply use solaris, hpux and so forth.
Here, I prepared an nfs server using ubuntu linux. Plain ubuntu linux, desktop edition.
1. Install the nfs server packages to turn your desktop into an nfs server.
$ sudo apt-get update
$ sudo apt-get install nfs-kernel-server
2. Prepare a directory to be shared. For testing, allow anybody to mount it and write into it.
$ sudo mkdir /share1
$ sudo chmod 777 /share1
3. Edit the /etc/exports file to share the directory share1 with everybody
$ sudo echo /share1 * >> /etc/exports
$ cat /etc/fstab
4. Start the nfs daemons and verify that nfs is working
$ sudo /etc/init.d/nfs-kernel-server start
$ sudo showmount -e
That is it; this is all it takes.