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The Open Hardware Monitor is a free open source software that monitors temperature sensors, fan speeds, voltages, load and clock speeds of a computer.

SpeedFan is a program that monitors voltages, fan speeds and temperatures in computers with hardware monitor chips. SpeedFan can even access S.M.A.R.T. info and show hard disk temperatures. SpeedFan supports SCSI disks too.

Core Temp is a compact, no fuss, small footprint program to monitor CPU temperature.

This is a port to OS X El Capitan 10.11 of MenuMeters by Alex Harper.

WinAudit is an inventory utility for Windows computers. It creates a comprehensive report on a machine's configuration, hardware and software. WinAudit is free, open source and can be used or distributed by anyone. IT experts in academia, government, industry as well as security conscious professionals in the armed services, defence contractors, electricity generators and police forces use WinAudit.

Mac OS X System Monitor and Process Explorer ToolatMonitor is the most advanced monitoring tool for Mac OS X that displays system activity in real-time. It is designed to allow quick assessment of computers state and it is powerful enough to make it a core utility in anyones system troubleshooting toolkit.atMonitor offers a better alternative to Apples own "Activity Monitor" and combines the best of the features of many other existing monitoring utilities. It also adds an extensive list of unique features of its own. In addition to the standard CPU, GPU, VRAM, FPS, Disk and Network info, atMonitor allows interaction with processes, setting up triggers, logging, purging RAM and much more. atMonitor can be displayed in the menu bar, as a stand alone floating window or in the dock icon. »

Real Temp is a temperature monitoring program designed for all Intel single Core, Dual Core, Quad Core and Core i7 processors. Each core on these processors has a digital thermal sensor (DTS) that reports temperature data relative to TJMax which is the safe maximum operating core temperature for the CPU. As your CPU heats up, your Distance to TJMax will decrease. If it reaches zero, your processor will start to thermal throttle or slow down so maximizing your distance away from TJMax will help your computer run at full speed and more reliably too. »

The BitBar app lets you put the output from any script or program right in your Mac OS X menu bar. And it's completely free. An impressive number of plugins have already been contributed by a wide range of developers just like you, and this site makes it easy to find them.

smcFanControl is the perfect application for all those Macbook owners getting burned by their hot-running Macbook.This Mac application allows you to control the speed of the fan in your MacBook so you can avoid it running hot.

XRG is an open source system monitor for Mac OS X. XRG allows you to monitor CPU activity, memory usage, battery status, machine temperature, network activity, disk I/O, current weather, and stock market data. The goal of XRG is to be a functional system monitor that has a clean and flexible interface, so it doesn't intrude on the rest of your Mac experience.

Using a database, it will show information about your SSD, such as the controller, processing tech, NAND type etc.Other useful information related to disk devices are also shown, such as S.M.A.R.T. status and partition layout.

Monitor numerous OS X statistics including: CPU activity System load over time Network bandwidth and activity Memory activity and usage Battery & wireless signal strength Disk usage Current time and date Compact, clever & fully customizable user interface Presents information both graphically and with text Beautiful on Retina display Fits in perfectly with the new system appearances Save & load custom appearances Minimizes impact on system performance View data on the desktop, in the menu bar or Dock Show & hide windows using system hotkeys »

MiniUsage displays various data like CPU usage, amount of network flow, battery status and process names which uses much CPU time in a menubar. It takes little space and can display various data, so it's suitable for notebook.

DriveDx is advanced drive health diagnostic and monitoring utility. Unlike most drive utilities, DriveDx does not only monitor the drive’s built-in S.M.A.R.T. status, but also analyzes the changes of all drive health indicators that are closely related to HDD or SSD failures (like the pending bad sectors, reallocated bad sectors, uncorrectable bad sectors, SSD wear out / endurance, and more) and alerts the user immediately if anything goes wrong. Our drive health diagnostics algorithms are based on the recent researches in this field. The application provides access to all sufficient drive diagnostic data to satisfy any system administrator. DriveDx is the first utility of its kind to have a real user-friendly Mac-style interface. »