Real-time performance monitoring, done right! http://netdata.firehol.org

Sysdig is open source, system-level exploration: capture system state and activity from a running Linux instance, then save, filter and analyze. Think of it as strace + tcpdump + lsof + awesome sauce.
With a little Lua cherry on top.

Lot's of tool to monitor your bandwidth

Monitor your bandwidth consumption

Software developers using Windows have a fantastic process explorer, made by Mark Russinovich. Linux lacks such a process explorer tool. This projects aims (in the end) to be an equivalent process explorer for Linux.

Goal is to have the same functionality of the Windows process explorer under linux, or less if linux limits us.

ntopng is the next generation version of the original ntop, a network traffic probe that shows the network usage, similar to what the popular top Unix command does. ntop is based on libpcap and it has been written in a portable way in order to virtually run on every Unix platform, MacOSX and on Win32 as well.