SpeedFan - Hardware monitor for Windows that can access digital temperature sensors located on several 2-wire SMBus Serial Bus. Can access voltages and fan speeds and control fan speeds. Includes technical articles and docs.
The Dude - MikroTik is a Latvian company which was founded in 1996 to develop routers and wireless ISP systems. MikroTik now provides hardware and software for Internet connectivity in most of the countries around the world.
Argus Monitor - Argus Monitor is for monitoring and analyzing the temperature and the health status of the hardware parts of the system.
Pandora FMS - Pandora FMS: Opensource monitoring software
Open Hardware Monitor - Monitors temperature sensors, fan speeds, voltages, load and clock speeds, with optional graph.
OpenNMS - Project home page of OpenNMS - a java based network managememnt platform developed under the Open Source model