Instead of an introduction, I'll answer the question 'Why did you left out wonderful applications like Scribus, Inkscape, Cinelerra, Wine, QCad etc?'. Well, because the article is about applications which I consider essential for daily use. Of course, some work with those every day, but not the majority. Secondly, if you ask why Amarok and not Banshee, or why KTorrent and not Deluge, well that's a personal preference. Unfortunately the article is about 10 and only 10 applications, so I can't include all of them here. Instead, I mentioned several (I know, not all) alternatives for each of the applications included here. Happy reading!