macOS cpu/mem monitor in system tray (menu bar)

I would like to monitor CPU and memory usage in realtime with charts on a macOS system tray (menu bar). Is there a utility that provides such functionality?

MenuMeters is popular among the Mac users I know.

For OS X 10.11 or later, use this fork of MenuMeters: http://member.ipmu.jp/yuji.tachikawa/MenuMetersElCapitan/

(Open the .prefPane file by Ctrl clicking and selecting Open.)

iStat Menus is an app by Mac / iOS developers Bjango, but it's not free ($16).

I also have the same needs but many such softwares are not free, thus I made one myself. Feedback is welcome.

https://github.com/ningt/iStats

This is an old questions, but newcomers might be interested in Übersicht. This allows you to display the information on the desktop, not the menu bar, much like in Conky.

Übersicht uses HTML5 web technology, so has a very modern feel to customize.