Essential NetTools is a suite of network and system tools. Although, as the name suggests, this application is full of network diagnostic and configuration tools, there are also plenty of system tools. The evaluation version has sixteen different diagnostic tools, most of them dealing with network diagnostics and monitoring.
The majority of the tools you get can easily be accessed from a command line, but Essential NetTools does a great job of providing a graphical interface for them. One example that comes to mind is NetStat, a very popular and sometimes essential Windows application. It allows you to check what incoming and outgoing connections are active at any given moment. Essential NetTools' version shows you all the active connections and shows what IP addresses they originate from, the type of protocol they are using and the IP they are calling; all in a neatly-organized screen.
Essential NetTools has the following tools: NetStat, ProcMon (process monitor), Ping, Traceroute, PortScan, HostAlive, EmailVerify, NSLookup, IPBlackList, NBScan, RawSocket, WiFIMan, Shares, NetAudit, SNMPAudit, and SysFiles. Some of them are for advanced users, but most are very easy to use and understand. All tools show stats in real-time, updated every few seconds, which you can change from the settings.