PingUin

An interactive monitoring utility that allows to watch the status of multiple servers including the hosting machine at once.

The most comprehensive, easy-to-use and visually impressive WPF-based network monitoring application that is completely open-source and modular.

Can be run as a windows service, acts as a server and allows remote HTTP management via browser, or can be run minimized, at background or from command line.

Generates impressive interactive charts, logs and statistics, supports exporting Excel-compatible reports, text and CSVs, SQL data or SQL-Insert statements.

Contains hardware information, bandwidth meter and usage, ping, whois, lookup, traceroute, port scanning, WOL (wake on LAN).

Allows users to develop custom plug-ins.

It's being developed in .Net 4, C# and Prism 4.