VMWare ESX has the vmkusage tool to collect and display performance data. When vmkusage is configured with vmkusagectl install, it will schedule cron jobs to get the performance data and to generate graphs. You can see the performance data using http://esxserver/vmkusage.
The freeware tool vmktree uses the same performance data but displays it better (screenshot). While the graphs in vmkusage are generated every 5 minutes, the graphs in vmktree are generated real-time. An interesting feature is realtime stats. It shows the result of esxtop in a browser window every x minutes.
