user_info is a class to retrieve information about the browser the user is using to access the current site script. It can analyze the user agent string sent by the browser in the current HTTP request and extracts the type of browser, user machine operating system, user machine IP address, accepted character set encoding, language name, and whether the user is a spider/bot.
vlogger is a logger daemon for Apache. It will accept piped logfile input, split it according to its corresponding virtual host (using a file cache to avoid resource limitations), and write it to disk. It automatically rotates all files and tracks them using timestamps. It is intended as a replacement for cronolog.
wtch periodically runs a shell command COMMAND and watches its output. When it changes it runs shell command ACTION. More precisely, it runs ACTION when a specified event occurs. The event can be a change of COMMAND's output, a change matching a certain pattern, or its negation, output equal to some previous output, etc. The output pattern defining an event is set by the --pattern option. By default, it simply detects any COMMAND output change.
xSH-Paranoia Patch is an project started for admins who work in large system environments. It allows you to see which user executes which command, when, where, and from what IP address. It logs everything to syslog, and with syslog-ng, you can log it to another machine where no user should/would have access. Currently supported shells are bash and tcsh.
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.