Assuming that you have an Ubuntu system with version 11.10 installed on it, the other necessary softwares to develop an Android Application are:
The Android SDK
Step 1: Download the Android SDK from here. Unzip the android-sdk_<machine-platform> file that you downloaded to a location of your choice, for example $HOME_DIR/android-sdk-linux.
Step 2: Update the Environment variables by editing the ~/.bash_profile or ~/.bashrc file and add the following variables:
Step 3: Install the Android SDK. Source the .bash_profile or .bashrc file to set the PATH. Invoke the “android” command from the command line without any options.
This launches the Android SDK Manager. Once the Android SDK Manager launches, select the SDK components that you want to install or update. You will need the Android SDK tools. Apart from that I recommend at least one version of the Google APIs by Google Inc. Here is a screenshot of what I have installed on my Ubuntu box.
PhoneGap is an open source mobile development framework and can be used to develop applications for iOS, Android, Windows Mobile, BlackBerry, webOS, symbian, and bada.
Step 1: Download PhoneGap from here
Step 2: Unzip the downloaded file callback-phonegap-<version>.zip to a directory of your choice, for example $HOME_DIR/PhoneGap
Apache Ant is a Java library and command-line tool that helps in building the application. Download the latest version from here. Unzip the downloaded file and include <ANT_HOME>/bin in the PATH, where ANT_HOME is the directory in which you unzipped the downloaded file.