NCMeters is a non-intrusive tweak for monitoring system vitals via Notification Center. It allows you to check CPU usage, memory and storage usage, and monitor both upload and download speeds.
NCMeters only runs when you have Notification Center open, so it's not going to be overly taxing on system resources when going about your daily business. To ensure accuracy, data is collected using traditional command line tools.
Along with those basics, NCMeters features quite a bit of customization. Have a look at our video walkthrough and see for yourself.