This is pretty much just like TPT, only that it is a separate program, or a TPT mode that can be set in the options menu.

So, it is basically just like Powder Toy, only it uses the whole desktop, including the desktop background, the icons and stuff... What you can do is that you draw the particles on the desktop, not just in a small crammed up window. It is basically just like Souptoys (ever heard of that game?), only it uses the basic TPT elements. There are two options in making this:

1) Desktop Mode

It is a mode to be activated on the options menu. The PRO in this is no need to do another program, only more code and stuff. (Will this option actually be possible?) The  CON is that there are almost limited options on the play mode, for example: If Desktop Mode comes with an option to let particles collide with desktop icons, widgets, etc., where would those options be? Would there be another button that would appear for Dektop Mode options?

2) Make a seperate program called Desktop Toy

This way, options just like the ones mentioned above can be added easily. The PRO here is that you can integrate more options and more features. The CON here is that coding may possibly start from scratch... Or maybe you can use some code from Powder Toy!

Notes:

- There could be an option to turn the taskbar into a void if the particles touch it. If the option is turned off, particles collide with the taskbar.

- Other programs can be run in the background (just like Souptoys) while playing. For example: A movie is running in the background while you are playing DT (Desktop Toy). Which basically means DT is an invisible window with only the elements and buttons showing. For DM (Desktop Mode), It will turn the TPT window invisible.

- Of course, you cannot interact with desktop icons and stuff while playing DT or using DM.

The options bar on upper right corner of TPT will appear on the upper right corner of the desktop. The elements menu is located on the upper left corner. The deeper options menu, such as the one on TPT (located beside the login bar) is a button on the options bar. So is the login, save, and load buttons.

- Would it be possible to load and upload DT saves online? (Only for DT not DM) It would be possible that this is impossible with DM.

- Pressing the ESC key will put DT on sleep mode, which is simply just minimizing DT. Pressing ESC twice quits DT. It would be possible that this is impossible with DM.

- All other TPT features  (console, display mode, debug mode, HUD, etc.) can be implemented as well (If possible).

- For some experience and to fully understand what I'm suggesting, try Souptoys: souptoys.com