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.
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.
zlog is a reliable, efficient, thread safe, flexible, pure C logging library. It was written because there were no good C logging libraries along the lines of Logback for Java or log4cxx for C++. printf can work, but can not be easily redirected or reformatted, and syslog is slow and designed for system use. It provides a syslog model, log format customization, multiple output, safe run-time reconfiguration, high performance, user-defined log levels, safe log rotation, a log4j-style key-value map, in-built debugging, and no external dependencies.
OtrosLogViewer (OLV) is software for analyzing an application's logs and stack traces. It loads logs from remote servers using ftp, sftp, ssh, samba and other supported filesystems, listening on a socket, or connection to a Log4j SocketHubAppender. Logs can be gzipped, and OLV will decompress them on the fly. Many log formats are supported (JDK logging, Log4j XML, and custom patterns). OLV allows log highlighting. Automatic log highlighting is based on string matches, regular expressions, or custom Java code. Notes can be added to log events. Display of message details can be customized by message formatters and a colorizer (i.e., formating SOAP request and highlighting XML syntax). OLV can be extended by plugins (filters, log parsers, log event markers, message detail formatters, and colorizers).
Analog PHP is a short and simple logging package for PHP 5.3+ based around the idea of using closures for configurability and extensibility. It functions as a static class, but you can completely control the handling of log messages through closures (aka anonymous functions), and it also comes with a dozen pre-written handlers. It is well-documented, with examples for each type of log handler, and ultra-concise. The core is literally only 43 lines of clear, non-obfuscated code, and the whole is only a fraction of the size of comparable packages (for example, 293 total lines vs 1021 for Monolog).