I'd like to be able to view my cpu and memory usage in real time. Not as a desktop widget or window application, but as a widget in the menu bar. Is this possible?
iStat Menus has the functionality you are asking for. It is available starting at USD$14.39 for a single license or $17.99 for a family pack (up to five different Macs).
I use MenuMeters for this functionality, and have a hard time living without it. How do other people know when their web browser is finally done downloading a page, or YouTube stalled out, or iPhoto still working, or ...?
MenuMeters is freeware, but well worth the donation.
The original author has stopped maintaining MenuMeters, but someone new has taken over for El Capitan.
Check out iGlance it's open source.
One that hasn't been mentioned yet is Stats, which describes itself as a
Simple macOS system monitor in your menu bar
It's an excellent open source project (https://github.com/exelban/stats) that can be installed via:
brew cask install stats
I made a simple app that displays cpu and memory usage on menubar, free and open sourced. Feedback is welcome.
I created a free app that shows percentage on the menu bar:
You can download it from here:
I prefer SystemPal. iStat itself consumes too much CPU and RAM. SystemPal is quick, tiny, configurable, neat, and powerful. It's available on Mac App Store.
A free open source solution is CpuInfo on GitHub (shows cpu only)
Or you can try some geeklets from the internet (or make one yourself) on Geektool. I find it more customizable than menu bar apps, and prettier when I get to use the fonts and sizes I like.
Haven't seen this one mentioned yet: Menu Bar Stats 3