While on my daily travels on thrawling through the Internet I sometimes come across a file/program which will remain forever on my hard disk (this is until I find a better one). Excellent applications are few and far between, on the other hand, totally resource hugging pieces of crap can be found anywhere. Anyhow, below is a small (very small) list of files which I find useful.

Putty - If you want a telnt client for M$ Windows (Puke!)    then this is the one to use.

nmap - Source code for the best port scanner available which allows you to check the security of your network.