- tcpdump/libpcap
- tcpdump and libpcap project page.
- netfilter/iptables
- Home to the software of the packet filtering framework inside the Linux 2.4.x and 2.6.x kernel series.
- Crypto++ Library
- A free C++ class library of cryptographic schemes.
- The GNU Crypto project
- Aims at providing free, versatile, high-quality, and provably correct implementations of cryptographic primitives and tools in the Java programming language for use by programmers and end-users.
- TripWire
- Tripwire provides configuration control for virtual and physical infrastructures while helping organizations successfully achieve and maintain IT configuration control.
- Security-Enhanced Linux
- Security-Enhanced Linux homepage.
- Top 100 Network Security Tools
- As title suggests.
- Route Views Project
- University of Oregon's Route Views Project homepage.
- IETF RFCs
- IETF Request for Comments page.
- The Hivelogic Enkoder
- The Enkoder helps protect email addresses by converting them into encrypted JavaScript code, hiding them from email-harvesting robots while revealing them to real people.
- GTools
- MD5 hash sum generator / encrypter.
- GnuPG
- GNU project's complete and free implementation of the OpenPGP standard as defined by RFC4880.