libKISSlog is a trivial lightweight C++ template library designed and written according to the KISS (Keep It Simple and Straightforward) principle. It leans heavily on STL for keeping its implementation as simple as its usage, and tries to provide C++ developers with a lightweight, paradigm-pure, and flexible alternative to logging libraries which use design and/or implementation decisions which at least the author of libKISSlog believes to be questionable. Its easiest to explain why libKISSlog would be suitable for your needs by listing the things which libKISSlog does not choose to use or do: no singletons or other forms of mutable global state, no macros, no attempt to fit the Java runtime everything model onto a C++ library, no attempt to be a Java-style (bloated) framework, no attempt to make the choice for you of whether you need thread safety, and no compromise on simplicity in order to facilitate questionable inner-loop logging practices.
Pantheios is a C/C++ logging API library. It offers an optimal combination of complete type-safety, very high efficiency, genericity, and extensibility. It is simple to use and extend, highly portable (platform and compiler independent), and it upholds the C tradition of only paying for what you use. Pantheios supports logging of message statements of arbitrary complexity, consisting of heterogenous types. Pantheios supports filtering of log messages based on severity level.
Just For Fun Network Management System is a PHP-based network management system that features an integrated syslog, Tacacs, TFTP configuration downloading, SNMP polling, SNMP traps, journalling, auto-discovery, performance graphs (RRD), SLAs, and a lot more. It uses MySQL or PostgreSQL as the backend and works under Linux and Windows.
NagiosAppender is a pure Java implementation of a Log4j appender that allows the developer/administrator to send log records to Nagios via the NCSA server (using the push model). It provides a simple solution for Nagios administrators whose only alternative is to implement a polling function against against the output of a standard Log4j appender. The log4j configuration file provides for user-specific mappings between Log4j levels and Nagios levels. The configuration file also allows the user to select whether to set the Nagios 'service' and 'host' programmatically via Log4j MDC, or via the config file. Later releases support XOR encryption.
TCPWebLog is a system that collects and aggregates Apache and Varnish Web server logs from multiple Linux computers. It uses a simple "client" program that pipes logs to a central server over a TCP connection, and a "server" program that receive the logs and quickly aggregates or splits them.