Download of iStatistica 6.2 for Mac was available from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The application is included in System Tools. This software for Mac OS X is a product of Andrey Tsarkov.
From the developer:
iStatistica is an advanced system monitor for macOS. It includes 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.
Mac system monitor provides an easy way to eject external drives, overview your battery statistics, realtime informations about cpu and ram usage and much more.
You may want to check out more software for Mac, such as iStatistica Sensors, which might be similar to iStatistica.