[SpikeProxy] SpikeProxy (Web Application Assessments) a HTTP proxy written in Python .

[WebScarab] OWASP WebScarab similar program in Java .

[Spike] Spike Fuzzer Creation Kit written in C with its own small scripting feature to fuzz block based network applications .

[SMTPfuzz] smtpfuzz.pl my own quick-dirty perl snippet to fuzz line based applications like SMTP .

[PROTOS] PROTOS PROTOS - Security Testing of Protocol Implementations, this site has many documents about fuzzing some Java programs .

[RATS] R.A.T.S. the Rough Auditing Tool for Security a source code auditing tool .

[DProbes] dprobes a pervasive debugging facility for linux from IBM (haven't used that one, but looks cool) .

[fenris] fenris a suite of cool tools (tracer, debugger etc.) .

[ngrep] ngrep ngrep homepage .

[TCPreen] TCPreen homepage TCPreen (TCP network re-engineering tool) .

[Webgoat] WebGoat a servlet (Java) based tutorial teaching the basics of web application security bugs (like SQL-Injection, XSS etc.) .