What is the smallest OS you know of, with a GUI, VPN client and a web browser? The best I have found so far is Puppy Linux, but can I go smaller?
The smallest operating system for the PC architecture i know of is MenuetOS (http://www.menuetos.net). It's written completly in x86 assembler and includes a TCP/IP stack, the assembler toolchain and a web browser. It fits on a single disc image. But it lacks the VPN feature, so you have to write it yourself in asm or try using something like hamachi as workaround.
Smallest OS I know is KolibriOS
It's about 1.4 MB (floppy disk size) and features a GUI.