Windows built-in Explorer, because of combination with browser and some fancy functions, sometimes its open-speed may be very slow, at this time you can try Mini Explorer (ME2 for short), this fast and lightweight Windows Explorer alternative.
Software's size and function are growing with each passing day, yet those small ones are always welcome by users. Foxit Reader and PDF-XChange Viewer have taken over the market of the bulky Adobe Reader at one time, but they also gradually lost the original lightsome look in the process of commercialization. In this trend, only SumatraPDF is still faithful to its original faith!
1by1 is an excellent audio player tool by Martin Pesch (its another quality audio tool is mp3DirectCut), know as its ultra small size and single-minded function. Compare with Winamp and many other mainstream audio players, 1by1 uses much less memory (run, play and minimize), and the gap is very obvious!
CutePDF Writer (formerly known as CutePDF Printer), after installed, it is equivalent to install a virtual printer driver (printer subsystem).
In order to protect the data security, we have to use some encryption softwares, but in so many such programs, of all, the best one has to be TrueCrypt who satisfies comprehensive functions, strong encryption ability and easy to use these three excellent conditions at the same time!