eCos (Embedded Configurable OS) is an open source, configurable, portable, and royalty-free embedded Real Time Operating System. It is written in C++, provides all the usual OS things. You configure the OS so that the parts you don't need aren't loaded to the embedded system. eCos is released under a modified GPL that allows for its use in embedded systems without having to GPL the embedded application.
Hwclock is a program that runs under Linux and sets and queries the Hardware Clock, which is often called the Real Time Clock, RTC, or CMOS clock. This is the program that most Linux systems use to get the time from the Hardware Clock and set the System Time at boot time. This program works on ISA (Intel), Alpha, SPARC, and M68K systems with or without /dev/rtc.
The NET-SNMP (formerly UCD-SNMP) package contains various tools relating to the Simple Network Management Protocol including an extensible agent, an SNMP library, tools to request or set information from SNMP agents, tools to generate and handle SNMP traps, a version of the unix 'netstat' command using SNMP and a Tk/perl mib browser. It was originally based on the Carnegie Mellon University SNMP implementation (version 18.104.22.168), but has been greatly enhanced, ported and fixed and barely resembles the original package anymore.
parapin makes it easy to write C code under Linux that controls individual pins on a PC parallel port. This kind of control is very useful for electronics projects that use the PC's parallel port as a generic digital I/O interface. Parapin goes to great lengths to insulate the programmer from the somewhat complex parallel port programming interface provided by the PC hardware, and comes as a user-space C library, or linked as part of a Linux kernel module.