Gridload collects data from your server or servers using a variety of different client applications. These clients are optimized to generate as little load as possible on the target machine being monitored. They connect to Gridload using the Gridload API, allowing you to create your own clients as well.
Currently supported clients are:
LoadAvg is free software that will change the way you manage your servers. Your server is a complex machine and you need to understand what keeps it running and what resources are being used in order to give it all shes got.
collectd gathers statistics about the system it is running on and stores this information. Those statistics can then be used to find current performance bottlenecks (i.e. performance analysis) and predict future system load.