iStat Menus

iStat is a series of system monitor apps. It’s available in different versions: iStat Menus, iStat for iOS and iStat Server as a companion application to the iStat for iOS app that lets you remotely monitor your computers (free for Windows and Mac).

CPU
Realtime CPU graphs and a list of the top 5 CPU resource hogs. CPU usage can be tracked by individual cores or with all cores combined, to save menubar space.
Network
A realtime graph to keep on top of what’s being sent and received for all network connections.
Date & Time
A highly configurable date, time and calendar for your menubar, including fuzzy clock and moon phase. A world clock with sunrise, sunset, moonrise and moonset times for over 20,000 cities. It’s one of the most powerful replacements for Apple’s date and time menu available.
Disk Usage
See used or free space for multiple disks in your menubar. More detail for all your disks is only a click away.
Disk Activity
Detailed disk I/O in your menubar, displayed as a graph, a variety of different read and write indicators, or both.
Sensors
Realtime listings of the sensors in your Mac, including temperatures, hard drive temperatures (where supported), fans, voltages, current and power. Fan speeds can be controlled, with different rules when on battery power, if you’d like.
Battery
Detailed info on your battery’s current state and a highly configurable menu item that can change if you’re draining, charging, or completely charged.
Memory
Memory stats for your menubar, shown as a pie chart, graph, percentage, bar or any combination of those things. The memory dropdown menu shows a list of the top 5 memory hogs, as well as other useful info.
Complete control
Each menu extra comes with many different display modes, customizable colours, font sizes and widths.