Download of DiskMonitor 1.2 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. Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. The actual developer of this free Mac application is IMO Systems Ltd.
From the developer:
DiskMonitor is a simple utility tool that shows the used storage space as a percentage on the stats bar. This updates every 30 seconds. It defaults to the main disk, but other storage volumes can be selected. Hovering over DiskMonitor's menu bar item will display the available space and the name of the disk volume.