Cool applications you use that others might not know of

[IYY]

Here are the rules:

1. No commonly used applications: This means, no Firefox, Gimp, Inkscape, Open Office, Beryl etc.
2. Application must be in the repositories (Kubuntu, Xubuntu, Feisty repos are all fine).
3. Application must be fairly easy to use, so that its usefulness can be quickly apparent.

Ok, so here are a couple of applications I've recently discovered that are truly amazing:

Qalculate!

This is without doubt the most powerful calculator I've ever used. And not only is it powerful, but it's also incredibly easy to use. It can not only be used for simple calculations, but also to factor, simplify, integrate, differentiate, sum, take means, calculate areas, do unit conversions, matrix multiplication... anything you can think of in the realm of math, science, engineering or finance. It even has a periodic table built in!

One thing I can tell you for certain: if I had this nifty little tool during my highschool education, I would not have learned anything, because it can do everything for me!

Even for simple calculations this tool is better than a regular calculator due to its intuitive interface that helps eliminate errors. For example, suppose I type in a slightly ambiguous expression like

12+5^2

as I type, text will appear underneath the input box telling me that the calculator understands the expression as

12+(5^2)

Makes you far more confident, and less error prone.

The program is available in both QT and GTK.

Agave

A far less ambitious program than Qalculate, but useful nonetheless. Agave is a colour scheme designer. You can pick a colour, and the program will show you its complement, split complement (a 3 colour scheme), triads, tetrads, an analogous scheme, or a monochromatic scheme.

So, if you are designing a webpage or a pamphlet, or even doing some digital painting, this program will tell you which colours go well together.

A tip: some people don't know that in GTK, you can drag and drop almost anything. So, you can grab a colour from The Gimp, drag it into Agave, and then drag and drop the complement of that colour back into The Gimp. Very useful.

Hydrogen

I am an amateur musician, but when it comes to electronic music I am twice as uneducated. Anyway, Hydrogen still managed to impress me. This application can be used to create drum and other percussion patterns. It's very easy to use (I figured it out instantly, with 0 experience in the field), and can be fun for those who have never played an instrument or done any work with sound.

It's a QT app, but looks equally good in both Gnome and KDE since it has its own theme anyway.

Zim

Zim is a desktop wiki. I guess it's very similar to Tomboy notes which you may be familiar with, but is designed for a more general purpose. You can create your own wikis (like Wikipedia) on your own computer, without using a browser, and with a very simple WYSIWYG interface. Can be handy to stay organized.

A GTK app.

Beneath a Steel Sky

This is an old cyberpunk point-and-click adventure game that has been ported (with ScummVM) to Linux. It's completely free, can be downloaded from the repositories, and even comes with speech (that is, every line of dialog in the game is spoken). The graphics are a bit dated, but the storyline is excellent. If you enjoyed games like Monkey Island, King Quest and Quest for Glory, you will love this one.

Ok... I'm done. Your turn!