iStat nano is an advanced system monitor in a tiny package. View detailed information on CPU, memory, hard drives, IP and external IP, bandwidth, CPU temperatures, fan speeds, battery, uptime and the top four processes. iStat nano features the lowest CPU usage of any stats widget we've seen (compare it if you don't believe us, I'm sure you'll be pleasantly surprised!).
What's new in iStat nano
Temperature monitoring for S.M.A.R.T capable hard drives (1 drive only)
Improved fan monitoring support for iBooks and PowerBooks