Logging solution by Pablo Costantini.

Main features:

• Multiple output levels (LOG, DEBUG, INFO, WARN, ERROR, FATAL)
• Inspection for Object and MovieClip types
• Multiple output targets using Publishers (similar to log4j)
• Flash 6 & 7 compatible. Flex is also supported.
• Small filesize, about 3kb with all available publishers.
• GUI Console for viewing and inspecting log messages.

Learn more about it on Pablo's blog entry.

An online example is available.