Coolplayer is a fast open-source audio player. It has a simple user interface and has a lots of skin support.

Miranda IM is an open-source multi-protocol instant messenger client for windows. It's smaller, faster and easier!
For more details on Miranda click here

Download:-
Miranda v0.8.5 for Windows
size 1.63mb

Sumatra PDF is a slim, free, open-source PDF viewer for Windows. Portable out of the box. Sumatra has a minimalistic design. Simplicity has a higher priority than a lot of features.
It's small and starts up very fast.

It's designed for portable use: it's just one file with no external dependencies so you can run it from external USB drive.

Bigzip is open-source compression utility tool based on Java.

7-zip is an open-source file archiver with high compression ratio with support for 7z, zip, gzip, tar files etc. It has been found that the compression ratio of the new 7-zip in the 7z format is lot better than the best known compression softwares like Winzip and WinRar!!

Features of 7-zip

Download:-
size 1mb
7-zip for windows