If you are a curious N900 owner and like to go a deep far and exploring the beast like me you should know about RPM and RA : 

Red Pill is an Application manager mode that disables certain safety features, and allows access to certain additional settings.

It changes the way Application manager behaves, primarily by removing many of the safety locks that prevent users from installing harmful packages, or upgrading or replacing important system packages (which can result in reboot loops). It also hides packages that aren't relevant to users, and shows additional settings to tweak specific behaviors (like whether to cache packages to the internal memory card during installation).

In the opposite way, while in the Blue Pill mode (the normal operating mode), Application manager has many safety locks in place to reduce the risk of the user accidentally damaging their tablet by installing harmful packages. So the App Manager will only show and let you install the packages which are meant to be installed by end users and have been "approved" for general access. Which is a good thing for majority of "average users". Red Pill mode disables these locks.

For the same purpose, in Maemo 5, Nokia has removed the ability to install standalone .deb packages, to make sure that only compatible and secure files can be installed via repositories.

To enable Red Pill mode:

Open Application manager and go to "Tools -> Application catalogue"
Click "New"
Type "matrix" into the "Web Address" field
Click "Cancel" (N900: tap outside the window)
Tap "Red" in the dialog to enabled Red Pill mode, or "Blue" to keep the Application manager as-is or to disable Red Pill.

You'll then get the "Install from file" option in App Manager's menu. Using it, you will be able to install standalone .deb packages downloaded from the Internet and stored locally on the device!

Ps : The Red-Pill mode is not persistent after being enabled. Closing the Application manager, disables Red Pill.

Anyway, similar function can be accomplished by Root access and rootsh can be installed via application manager (if you have Extras enabled).

In the same way, having root access is an important step for users interested in modifying things "under the covers" of their tablets; without it, you won't have the necessary permissions to make those modifications. Root access is disabled by default on new tablets. Thankfully, the steps to enable root access are simple.

Root access is not required to install additional applications through Application Manager, open X Terminal or use your tablet in day-to-day operation.

If you want to edit the underlying system configuration, install applications through the command line or other low-level tasks, you will require root access. Then, from the shell, run sudo gainroot (or root for short). This will give you a root shell

WARNING: The steps described on this page could lead to severe damage to your system and/or device. Proceed at your own peril

Seen at my-maemo and wiki.maemo