There are a lot of freeware applications availaible for S60 phones and my favourite is ofcourse FExplorer. I see that I'm so dependent on it as it lets me tweak my phone. It is a must for an advanced user. One can also manually remove malware (if he knows how to do that) and do lots more. But for newbies, it can be dangerous as it exposes the system files and one wrong move can damage the phone. Don't know why people recommend it to them just like that.

Many users are not even aware of all freewares availaible. Here is a great list of such applications for them - http://www.simonjudge.com/s60freeware.html .