Performance is too general high level term, can you specify what exactly you need to monitor ? On the other hand, a tool similar to the above ones is "sar" - system activity report, part of "sysstat" package.
No specific requirement for the time being. Just found it on Internet googling. Neither I have deep knowledge on this package. Before starting injecting effort on it I expect to know whether there are better alternatives avoiding spending time and effort on secondary tool.
yes, this is one of the many pages for sysstat, this will fully substitute nmon tool, which, as far as I know, is available only for AIX. What is your flavor of UNIX ?