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.
CleanMyMac X - Clean, protect and speed up your Mac
Open Hardware Monitor - Monitors temperature sensors, fan speeds, voltages, load and clock speeds, with optional graph.
DaisyDisk - DaisyDisk is a disk analyzer tool for OS X that visualizes hard disk usage and allows to free up hard disk space.
xScan - xScan is an application for viewing the behavior of your computer and Mac.
Fossils - Find and clean out all your old unused files