(Commands are given assuming an Ubuntu 11.10 machine)
Rake is needed to build the front-end: sudo apt-get install rake
You'll need the haml Gem to compile haml templates: sudo gem install haml
Jammit is needed to package assets: sudo gem install jammit
FSSM is needed to monitor changes in the Web front-end files and recompile everything: sudo gem install fssm.
You'll also need the NodeJS Package Manager (npm) to be able to compile Less CSS files and Coffee Script:
sudo apt-get install npm
npm install coffee-script
npm install less
By default the binaries are installed to $HOME/bin. Ensure that this folder is on your $PATH !
The data is stored in Mongo DB, so you'll need to install it too: sudo apt-get install mongodb.
MongoDB listens to 127.0.0.1 only by default. The Java components are connecting to localhost. Depending of your system configuration localhost can mean different things. If you encounter connection issues while building the Java components here are a couple of things to try:
- On some Ubuntu systems an alias is set to your hostname on 
127.0.1.1in/etc/hosts. If you encounter connections problems, it's the first place to look at. You should be able to safely delete the127.0.1.1line in/etc/hosts. - Edit your MongoDB configuration (
/etc/mongodb.conf) and comment thebind_ipline, then restart MongoDB. It should now listen on all interfaces and connection should succeed regardless of the IP address used. 
To build the Java components, you'll need Maven: sudo apt-get install maven2
Go to the web-front/ folder and use: rake.
Go to the root folder, and: mvn clean install.
To start the whole stack: mvn -f web/pom.xml exec:java -DfrenchTtsUrl=http://localhost/
(TODO: Document the frenchTtsUrl property.)
This will start a webserver on port 8999. Try http://localhost:8999/index.html
You can also start rake on a separate terminal to monitor your changes in the front-end code and re-publish them:
cd web-front/
mkdir public
rake watch