Since there doesn't seem to be a Telescope-dedicated post and I felt that we were hijacking the other thread I thought I'd start one here.
(Note: I have nothing to do with the app development, just a user) - the developer is Mitrandir .

What is Telescope?
Telescops is an Application switching tool for OS2008.
Simply explained - you press one key (the 'home key'/F5 (the upper hard-ware key on the left side of your tablet)) - and all applications you are running shows as thumbnails on a screen and you can there easily select what app to jump to.

Since a picture is worth a thousand words: Telescope Promo VIdeo: http://www.youtube.com/user/DenielOl.../2/6FhOf4evqtU

Great, where do I find Telescope?
Garage page: https://garage.maemo.org/projects/telescope

Note: Dependencies will NOT be automatically installed when installing the .deb-file from the garage page. However, all dependencies are available in the Extras repository.

Installing from Extras-Devel: http://skriblovsky.net/maemo/telescope.install
Note: This install-file will add the Extras-Devel repository to your device and the nature of Extras-Devel is that it is still in development and you are yourself responsible for accepting that risk and any issues that may come along.


=====
Update 7/9/10
Telescope 0.2.9
D-Bus support. Telescope can now be called by D-Bus method call:
bus: org.telescope
path: /Telescope
method: org.telescope.Telescope.Show (or Hide)
Next version of Diablo5 theme will include statusbar applet for calling task switcher (like in Fremantle)
Workaround for liqbase applications. They will be iconified when telescope appears


Update 7/1/10
Telescope 0.2.8

• Huge source code refactoring. I think around 40-60% of source code was refactored in order to improve internal logic of the application, eliminate potential bugs and make it more easy to bring enhancements in future
• It's now possible to move selection with joystick if you put following into your /etc/telescope.keys:
  
  Code:

  press(Right):  internal(selectRight)
  press(Left):   internal(selectLeft)
  press(Up):     internal(selectUp)
  press(Down):   internal(selectDown)
  press(Return): internal(switchToSelected)

• Several potential bugs was fixed
• Added a couple of config-options for one guy who tries to adopt Telescope on Ubuntu on N8x0

Update 6/2/2010
Telescope 0.2.7.2
Workaround for OSSO MediaPlayer. Exactly as maacruz suggested -- when user is calling telescope from mediaplayer, mediaplayer will be minimized to hide its video overlay. When video is active, mediaplayer minimizes without animation, so it does it fast.


Update 5/31/2010
Telescope 0.2.7
Support for SDL games and other non-standard windows, for example MPlayer, links2 and others
Changing of window title is now displayed in real time when telescope is active.

Update 5/23/2010
Telescope 0.2.6.2
Several bugfixes:
* Window titles disappearing after screen rotate
* Active window not always highlighted
* Window preview is invalid sometimes


Update 5/12/2010:

Below, Telescope and 6 open apps:

(The screenshot is from an N810 running Diablo and the Diablo5 theme).