Hi Linda,
Both rcli and VMA are providing an interface to control/manage your VMware ESX and/or ESXi servers remotely using the command line. The vMA is a fully packed, ready to run virtual appliance. The rcli can be installed on Windows or Linux. VMware renamed the cli to vSphere cli...
RHEL=Red Hat Enterprise Linux
Putty is a very good, opensource secure shell client. General purpose, can be used for ESX too, but the ESXi version does not (officialy) support remote connections using a SSH client.
Regards, Ronald