What are the best Ubuntu/Debian tools and Open Source applications for young learners at Elementary School?

Hello,, everybody.

I'm interested in Open Source software at School, specially in Debian/Ubuntu.

For example. We've got a very good free educational tool: GCompris.

And here's a wonderful one to make animations and games we can easily share: Scratch

We can download the alpha version of the Scratch 1.4 package for Ubuntu 9.04:

http://info.scratch.mit.edu/Linux_installer

And this is the scratch-1.3.1_0.9-4_i386.deb link (an older one):

http://info.scratch.mit.edu/@api/deki/files/779/=scratch-1.3.1_0.9-...

Well,... We can also download it for Windows / Mac, but...

http://scratch.mit.edu/

What other Ubuntu/Debian tools and Open Source programs do we use at Elementary School?

Help me, please. I'm looking for them. Thanks.