XMeters!

Rainmeter is a desktop customization platform. Through Rainmeter, you can enhance your Windows computer at home or work with skins: handy, compact applets which float freely on your desktop, much like Windows Sidebar gagdgets, or dashboard widgets for the Mac. Rainmeter skins provide you with useful information at a glance. Its easy to keep an eye on your system resources, like memory and battery power, or your online data streams, including email, RSS feeds, and weather forecasts. Many skins are even functional: they can record your notes and to-do lists, launch your favorite applications, and send your tweets to Twitter - all in a clean, unobtrusive interface that you can rearrange and customize to your liking. »

SidebarDiagnostics - A simple sidebar for Windows desktop that displays hardware diagnostic information.

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

GeekTool is an application for Mac OS 10.6+. It lets you display various kinds of information on your desktop via 3 default plug-ins: