GWT (Google Web Toolkit), is a development toolkit for building web applications.
You can have a look at the Getting Started page for a basic knowledge. Installation too is easy enough.
Pre-requisites for Installation
1. OpenJDK Development Kit (JDK) version 1.5 or later
2. Apache Ant
1. Install Eclipse or Netbeans. I am using Eclipse.
2. Install the Eclipse-plugin. Refer http://code.google.com/eclipse/docs/download.html.
3. Install the GWT SDK. Refer http://code.google.com/webtoolkit/gettingstarted.html#installing.
Getting Started With Applications
Refer to the following pages.
1. Getting Started With GWT SDK
2. GWT In Action
[Note: Install JDK, Apache Ant and Eclipse (or NetBeans) using apt-get or Synaptic Package Manager (or from Ubuntu Software Center for Ubuntu 9.10 and later).]