Snort is a network intrusion detection and prevention system. It is the most widely deployed technology of its kind in the world. It performs detection using a variety of methods including rules-based detection, anomaly detection, and heuristic analysis of network traffic. Its rules language is open source and available to the public as well.
HAproxy is a high-performance and highly-robust TCP and HTTP load balancer which provides cookie-based persistence, content-based switching, SSL off-loading, advanced traffic regulation with surge protection, automatic failover, run-time regex-based header control, Web-based reporting and management interface, advanced logging to help trouble-shooting buggy applications and/or networks, and a few other features. Its own event-driven state machine achieves 100,000 connections per second and surpasses GigaEthernet on modern hardware, even with tens of thousands of simultaneous connections.
BalanceNG is a modern, IPv6 capable software IP load balancing solution. It is small, fast, and easy to use and set up. It offers session persistence, different distribution methods (Round Robin, Random, Weighted Random, Least Session, Least Bandwidth, Hash, Agent, and Randomized Agent) and a customizable UDP health check agent in source code. It supports VRRP to set up high availability configurations on multiple nodes. It supports SNMP, integrating the BALANCENG-MIB with Net-SNMPD. It implements a very fast in-memory IP-to-location database, allowing powerful location-based server load-balancing.
Pen is a load balancer for "simple" TCP-based protocols such as HTTP or SMTP. It allows several servers to appear as one to the outside. It automatically detects servers that are down and distributes clients among the available servers. This gives high availability and scalable performance.
Keepalived for LVS aims to add a strong and robust keepalive facility to the Linux Virtual Server project. This project is written in C with multilayer TCP/IP stack checks. It implements a framework based on three family checks: Layer3, Layer4, and Layer5. This framework gives the daemon the ability of checking a LVS server pool states.When one of the servers in the LVS server pool is down, keepalived informs the Linux kernel via a setsockopt call to remove this server entry from the LVS topology. In addition, it implements a VRRPv2 stack to handle director failover.
GKrellM is a GTK-based stacked monitor program that charts SMP CPUs, disks, load, active net interfaces, and internet connections. There are also builtin monitors for memory and swap, file systems with mount/umount feature, mailbox checking including POP3 and IMAP, clock/calendar, laptop battery, sensors (temperatures, voltages, and fans), and uptime. It has LEDs for the net monitors and an on/off button and online timer for PPP. There is a GUI popup for configuration, plugin extensions can be installed, and many themes are available. It also features a client/server monitoring capability.
rsync is a replacement for rcp (and scp) that has many more features. It uses the "rsync algorithm" which provides a very fast method for remote files into sync. It does this by sending just the differences in the files across the link, without requiring that both sets of files are present at one of the ends of the link beforehand.
iptables is built on top of netfilter, the packet alteration framework for Linux 2.4.x and 2.6.x. It is a major rewrite of its predecessor ipchains, and is used to control packet filtering, Network Address Translation (masquerading, portforwarding, transparent proxying), and special effects such as packet mangling.