Hard Disk Sentinel is a hard drive monitoring and analysis tool. It allows you to determine the status of your hard drives and to measure their performance. It works with both regular, mechanical hard drives and the newer SSD alternatives. It can display quite a bit of information about hard drives. In case of mechanical drives and SSD drives with the appropriate drivers, it can display the temperature and overall health, by using the S.M.A.R.T. algorithm. I tested it with a virtual HDD inside a virtual machine, so, obviously, that information wasn't displayed.
The overview tab of this app shows a summarized analysis, showing temperature, health, and power on time and estimated remaining time. Of course, these values can vary, but it is nice to have an estimate. Also, from the main window, you can see free space on all your drives. The tab that I liked the most is "Disk Performance". It shows both real-time data and averages of your hard drives. I like the fact that it displays a transfer rate and activity meter for hard drive read and write operations. It also shows max speeds logged and it can estimate a max transfer rate by carrying out some tests.