AIDE (Advanced Intrusion Detection Environment) is a file and directory integrity checker. It creates a database from the regular expression rules that it finds from the config file. Once this database is initialized it can be used to verify the integrity of the files. Several message digest algorithms are used. All of the usual file attributes can also be checked for inconsistencies.
EtherApe is a GNOME/pcap-based etherman, interman, and "tcpman" clone. It displays network activity graphically. Active hosts are shown as circles of varying size, and traffic among them is shown as lines of varying width. It supports Ethernet, FDDI, Token Ring, ISDN, PPP, WLAN, and SLIP transports. It knows about VLANs, IP, IPv6, TCP, UDP, FTP, and a number of other protocols. Additional statistics windows will let you concentrate on protocols or nodes.
di is a disk information utility that displays everything that df does and more. It features the ability to display your disk usage in whatever format you prefer. It also checks the user and group quotas, so that the user sees the space available for their use, not the system wide disk space. It is designed to be highly portable across many platforms and is great for heterogenous networks.
Oak monitors syslogs from a collection of servers, and notifies the operators when problems arise. In addition to providing immediate notification of critical issues, it will also batch less critical problems into summary messages, which can be sent less often, and via any medium. It is part of the 'ktools' collection of network administration utilities.
Streamline is a pipelined I/O subsystem for both kernel and application processing on Linux, with 40+ filters for pattern matching, stream reassembly, compression, etc. It exports the pipes, sockets, and pcap interfaces and uses shared memory to reduce I/O copy and context switch cost. Logical uses are rapid application development of intrusion detection systems and similar complex network processing tasks.
nexB OpenAssets is a tool for inventorying, managing, and monitoring applications, software, hardware, networks, and generally any IT asset. It is designed so that system administrators, IT, and finance can determine what they have, how it is configured, what it is used for, and how much it is being used, so that informed decisions can be made. It complements existing network management software, integrates with a growing number of protocols and tools, and features no-agent discovery and inventory, configuration management including dependencies and correlation, monitoring, and reporting. It makes extensive and innovative use of XML, Xpath, and Xquery.
powermated is a program for controlling X applications and command line programs, and for monitoring various aspects of your computer with the Griffin PowerMate USB dial. It can update the PowerMate's LED based on different system monitors (such as CPU usage, XMMS/BMP sound output, and system mixer volume). It also has XOSD support for nifty on screen status displays.
GNOME Sensors Applet is an applet for the GNOME Panel to display readings from hardware sensors, including system and CPU temperature, fan speeds, and voltage readings under Linux via the hwmon and i8k kernel modules. It has a highly customizable display and an intuitive user interface.