iStat Menus - "An advanced Mac system monitor for your menubar."
CPU-Z - CPU-Z is a freeware that gathers information on some of the main devices of your system : Processor name and number, codename, process, package, cache levels.
Process Explorer - The top window always shows a list of the currently active processes, including the names of their owning accounts, whereas the information displayed in the bottom window depends on the mode that Process Explorer is in: if it is in handle mode you'l…
Speccy - Speccy - find the details of your computer's specs. Great for spotting issues or finding compatible upgrades. Download the latest version free.
MenuMeters for El Capitan - MenuMeters for OS X El Capitan 10.11 (and later)
AIDA64 - AIDA64 is a system information, diagnostics and benchmarking solution for Windows PC.