Having created several bootable Windows CD-ROMs with Bart's PE Builder, I thought how nice it would be if I could use some of the plugins on running systems (i.e. without having to reboot). So in spring 2004 I started searching the Internet for useful utilities that can be run directly from CD-ROM. These were my requirements:

Must be available free of charge (at least for non-commercial use). If source code is available under a Free Software/Open Source license, that's even better.
Small is beautiful
Graphical user interfaces are nice (this is Windows after all...
My focus is on diagnostic, network and security tools (no games or MP3 players...)

Here's my list. Download the tools, exctract the archives to a folder on your harddisk and burn them on a CD-ROM. Or put them on your USB-stick. If you leave out all unnecessary files (documentation, language files, etc.) and compress all executables with UPX, all these tools together (more than 600 executables) take less than 100 MB of disk space.

http://www.dirk-loss.de/win-tools.htm