Windows Utilities

Windirstat: Utility to visually display disk space useage. windirstat.info
Paint.net: Replaces windows paint. Actually useful. (Requires .NET framework 2.0 or higher.) getpaint.net
CPU-Z: Gathers information on some of the main devices of your system. cpuid.com
CPUCount: Detects number of processors, number of cores, hyperthreading capabilities. intel.com
InterBase PLANalyzer: Helps diagnose query complexity and performance issues. embarcadero.com
Virtual Null Modem: Emulates two serial ports connected via a null modem. VirtualNullModem.zip
Serial Port Monitor: Intercepts and analyzes serial data transfer between any serial device and Windows application. SerialPortMonitor.zip