LWServer is a small, quick and efficient multipurpose server, which your can enable and disable instantly:

1. A HTTP/S proxy server that allows websites or other users to use your PC as a middleman (which can bypass websites that block their own IP addresses)
2. A SMTP server/emulator that allows testing mail clients by letting them use your PC as a mail server, thus displaying the messages and optionally even send them away

The program is not just portable but also embeddable in other programs (see it for example in LWBlat GUI).
In a possibly unique fashion, the server supports not just TCP but also UDP connections, which can be tested for educational reasons.