Sometimes you might need an application which can't be found in the Ubuntu Software Center or Applications Directory. Then one of the following website might provide the application you are looking for:
"GetDeb is an unofficial project with the mission to provide the latest open source and freeware applications for the current Ubuntu Linux release, in an easy to install manner.The GetDeb repository extends the official repositories by providing latest versions and new applications. Unlike the official packages, GetDeb packages do not have a predefined release schedule - new software versions are provided as they become available from their authors. There is a short and limited testing phase instead of a full testing cycle to ensure packaging quality, however it is less strict than Ubuntu's official requirements.
"SourceForge is dedicated to making open source projects successful. We thrive on community collaboration to help us create the leading resource for open source software development and distribution. With the tools we provide, 3.4 million developers create powerful software in over 324,000 projects. Our popular directory connects more than 46 million consumers with these open source projects and serves more than 4,000,000 downloads a day. SourceForge is where open source happens."
"Freecode maintains the Web's largest index of Linux, Unix and cross-platform software, and mobile applications. Thousands of applications, which are preferably released under an open source license, are meticulously cataloged in the Freecode database, and links to new applications are added daily. Each entry provides a description of the software, links to download it and to obtain more information, and a history of the project's releases, so readers can keep up-to-date on the latest developments."
"Community Portal for Applications Apps GNOME, GTK+ Linux Multimedia Graphic Development Utilities Screensaver as a part of openDesktop.org, which is the umbrella site summarizing the content of all the sites in the network. Oncluded in this networks are sites such as KDE-Look.org, KDE-Apps.org, GTK-Apps.org, GNOME-Look.org and many other similar sites."