The device tool is a java program. Install java on your PC. Without the servers, the original data on the tablet will be lost, but there are still apps and the like available (e.g see App Gallery | webOS Nation )
Tip: How to Bypass Activation | pivotCE
Skip through this post: HP TP Server Error to the bit that says "Almost done..." and note from Step 4, the command line instruction to run the device tool. You either navigate to the folder where you put the program (e.g. Downloads) or specify the path to that folder in the command (see the example). To navigate, you only need the commands, 'ls' (list) & 'cd' (change directory). For example, if you type, ls and the list includes the folder, Downloads, you can then type cd Downloads to open that folder. ('ls' to view contents, 'cd ..' to go back up the file structure. Once the device tool is run, you should be good to go.
Booting into Recovery Mode
(...)boot the device into recovery mode by performing the following steps:
- Plug the USB cable into your computer. Do not connect the other end to your device yet.
- Remove the battery from the device.
- Hold down the device's volume up button.
- Insert the USB cable into the device.
- Re-insert the battery.
- Release the volume up button.
The device will boot into recovery mode, and you will see the USB logo on the device's screen. At this point, you may run either the webOS Doctor (to flash your device with the latest version of webOS) or the activation-bypass tool (to enable your unactivated device for development).
Guide: Coming (Back) to webOS in 2014, Part 1 | pivotCE
Apps: webOS & LuneOS Apps on Preware Catalog (includes apps from this site's gallery)
See also the links in my signature. Especially the last two.
Other OSes you can install are Android and LuneOS (which is the new version of webOS - still in development). I think Ubuntu & Arch are also possible.