PHREL is a per host rate limiter. It will track the rate of incoming traffic on a server and insert a chain into iptables when a configured threshold is crossed. The inserted chain may either rate limit or block the offending host for a period of time. The inserted chain is automatically removed when the offending host's traffic levels return to normal. PHREL is particularly well suited to protecting nameservers (DNS) from random hosts that flood requests, and to preventing SSH brute force login attempts.
conntrack-tools is a set of userspace tools for Linux that allow system administrators to interact with the Connection Tracking System, the module which provides stateful packet inspection for iptables. It includes the userspace daemon conntrackd and the commandline interface conntrack.
The Userspace Logging Daemon (ulogd) is a flexible framework for extensive logging of packets on a firewall machine. ulogd uses the ULOG target of iptables/netfilter, the packet filtering framework of Linux 2.4 and 2.6. It supports binary plugins for adding packet interpreters and output-targets (e.g., for logging into databases, user-defined filetypes, etc.).
Dante is a free implementation of the proxy protocols SOCKS version 4 and SOCKS version 5 (RFC 1928). It can be used as a firewall between networks, controlling outgoing traffic. The package consists of two parts: a socks server and a proxy client that supports socks, HTTP proxies, and UPnP. RFC 1961 (GSSAPI) is supported in both the client and the server. Commercial support is available.