Most people will probably want the tarball of the latest release, xfce4-hdaps-0.0.6.tar.gz. The latest version will always be kept in git.
xfce4-hdaps is included in the following Linux distributions:
A plugin to indicate the status of the IBM Hard Drive Active Protection System, or HDAPS.
As of Linux kernel 2.6.28, a kernel patch is no longer required to support the HDAPS functionality. As a result, this plugin will only (officially) support kernels newer than 2.6.28.
It will also only (officially) support the hdaps module provided by the tp_smapi project. The tp_smapi module is currently recommended by the hdaps devs, so you should be using it. In the future, the in-tree module will probably be supported as well.
Oh, and you'll need to be running the hdapsd daemon which updates sysfs with the values read by the plugin. I mean, it's not necessary, but it is if you want the plugin to do something.
I think it builds like most XFCE panel plugins. Git users, run './autogen.sh' in the project directory, and hopefully it will do whatever it does to make your project directory look like the tarball release. If it does (or if you just downloaded the tarball), run,
./configure make
With any luck, you will have an xfce-hdaps executable in your panel-plugin directory.
Now, there should also be an xfce4-hdaps.desktop file in the panel-plugin directory. You need to copy this to the directory where XFCE keeps all of those things. For example, the system-wide location on Gentoo is /usr/share/xfce4/panel-plugins/.
Finally, modify the X-XFCE-Exec parameter in the desktop file to reflect the real location of your xfce4-hdaps binary. You should now be able to add the plugin to your panel.
This is the frequency with which the plugin checks the status of HDAPS. If you set it to 500ms (the default), it will check every half second and update the icon according to what it finds.
The name of the device whose HDAPS status you wish to monitor. This will almost certainly be a hard drive, and will most likely be "sda". With any luck, the plugin will auto-detect the supported devices on your system. If you have more than one supported device, you will need to select it on the configuration dialog.
Email them to me at that address on the home page.
If you can't figure out how to work this, you're probably (one of the following),