iStatistica is an advanced system monitor. It includes a Notification-Center widget and status-bar menu. Simply slide out Notification Center to keep an eye on your CPU, memory, disk usage, and network activity. 
Features
System monitoring
uptime memory pressure CPU usage disk usage Battery information
uptime cycles health capacity Network activity
network map external WAN IP internal LAN IP address router IP address incoming and outgoing traffic speed Temperature and Fans*
CPU, GPU, memory temperature statistics Fan speeds
II. Instruction
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