LiMon (Linux Monitor) is a free/open/libre multiplataform real time Linux monitor written in C/C++, and other languages. Monitor of server's relevant aspects, such as services, temperature, CPU, memory and disk usage, etc.
sysprofd is a system profiling daemon that can report results through a tcp connection to a remote client. sysprofd profiles cpu, memory, and swap usage statistics, process status statistics e.t.c. Imagine using it to easily monitor lots of linux boxes