Nitro is simple, fast and powerful. It can synchronize your appointments on the cloud with Ubuntu One and Dropbox, so you can access them from any computer, not lose any of your tasks and you’ll never get a conflicted copy. Nitro also creates a todo.txt file so you can see or embed your tasks in plain text. Nitro is available for a variety of platforms such as Linux, Mac and as extension of Google Chrome / Chromium. And the development team is working on mobile versions and so they’ll be available in the futureFind me on Google+
Ubuntu software repository is one of the bigger, and this means that you can easily install a lot of software with the Ubuntu Software Center or from the command line with a simple
sudo apt-get install softwarename, but sometimes you want a software that is not present or perhaps a newer release of the one available in the main repository, in this cases you can use a PPA.
A Personal Package Archive (PPA) is a special software repository for uploading source packages to be built and published as an APT repository by Launchpad or a similar application, once is published anyone can use it and install software from there, just keep in mind that once that you add a PPA you “trust” the software published from that source, so add PPA only when really needed and only from known and safe sources.
Y PPA Manager is a software that can help you in manage,add,remove and search easily PPA in your Ubuntu.