whats the most useful app?

Not sure of the policies on necroposting here but what the hell. The single most useful app is your web browser (I prefer Opera but the choice is yours) because its the app which allows you to obtain every other app. After that I'd say your torrent client (mine is utorrent) and jdownloader, for similar reasons (but you need to browse to find the torrents and ddl links), WinRAR and Daemon Tools and ImgBurn for dealing with files you've downloaded. And after that it fans out depending on what it is you're into.

When I saw the title, I thought "yet another iPhone/Android thread"? Anyway, I see most people have mentioned more than one program here, and rightly so. My basic setup is almost the same as temisturk's, except that I use 7-Zip instead of WinRAR, and PowerISO for image files. (Nice to see you use Opera as I have for over five years now. Seems we're a minority :)) Then there's CCleaner, Defraggler for basic maintenance, Total Commander which I began using again this year, Radmin and Filezilla server for passing stuff to and from my netbook/improvised NAS, MPC-HC and ffdshow-tryouts for movies, jDownloader, SABnzbd, and uTorrent for downloads, and some others.

A browser is fine:

If you don't have much for digital assets of your own.

Without thousands of your own video to sample, then you don't need this app. But I do.

Without thousands of family pictures to randomly view and share, then you don't need this app. But I do

Without years and years of notes, emails and URL's to recall, then you don't need this app. But I do.

Without a large music / audio collection to browse, then you don't need this app.

If you are not interested in hunting for Faster Than Sight objects, then you don't need this app. But I do.

If all you want to explore; is other peoples data, then you don't need this app.

i am unable to understand what kind of application you are talking about...but i would like to tell that i like Windows Media Player 11.....

This is so general question , there is a useful app for each task

Maybe the most useful app/software would be the OS

Mozilla Portable
7-Zip
PowerISO
Aimp
Gom
Daemon Tools
utorrent
ccleaner
Filezilla
Eset 5