Although I'm unaware of a single cli based program that will provide all the information you requested, there are dozens of tools that can give you a good idea as to the state of the server. Some of the more common of these are:
ps (try ps auxf),
top (sort running processes by their cpu usage, memory usage, running time etc),
netstat (try netstat -taunp),
w (see who is logged in and what they're doing).
For more interesting hardware monitoring, on Ubuntu you can use the sysstat package to provide commands such as
vmstat (memory) information for monitoring physical hardware.
Finally, there are a number of tools available which allow you to setup a web interface to perform monitoring of your server which can provide data you are specifically interested in (CPU utilisation, memory usage, disk io, network io, "number of emails sent", "number of records in a particular table") using one of many monitoring tools. I'd suggest Nagios as a starting point.