SystemExplorer!

Process Hacker is a feature-packed tool for manipulating processes and services on your computer. A free and open source process viewer with powerful process termination and memory searching/editing capabilities.

Windows Task Manager is a task manager application included with Microsoft Windows NT family of operating systems that provides detailed information about computer performance and running applications, processes and CPU usage, commit charge and memory information, network activity and statistics, logged-in users, and system services. The Task Manager can also be used to set process priorities, processor affinity, forcibly terminate processes, and shut down, restart, hibernate or log off from Windows. »

Glances is a CLI curses based monitoring tool for GNU/Linux and BSD OS. Glances uses the PsUtil library to get information from your system. It is developed in Python.

WinSpy++ is a handy programmer's utility which can be used to select and view the properties of any window in the system. WinSpy is based around the Microsoft Spy++ utility that ships with Microsoft Visual Studio.

System Monitor is a tool to manage running processes and monitor system resources.

Easy to use application for monitoring and controlling running processes.

This tool controls programs, disk, CPU. Replace task manager, tweak and tune up XP or Vista. Speed up windows startup. Get rid of spyware and viruses.

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. »

Resource Monitor is a system application in Microsoft Windows operating systems. It is used to view information about the use of hardware (CPU, memory, disk, and network) and software (file handles and modules) resources in real time. Resource Monitor is available in Windows Vista and onwards only (In Windows Vista, it is known as Reliability and Performance Monitor). Resource Monitor can be launched by executing resmon.exe (perfmon.exe in Windows Vista). It was also on Windows 95, 95 OSR, 95 OSR2, 98, 98SE, ME, and NT. »

Image Hijacker is a small and easy to use application that allows you to run a program via another one to hide it from prying eyes.

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 »

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.