log2timeline is a tool designed to extract timestamps from various files found on a typical computer system(s) and aggregate them.
The initial purpose of plaso was to collect all timestamped events of interest on a computer system and have them aggregated in a single place for computer forensic analysis (aka Super Timeline).
However plaso has become a framework that supports:
adding new parsers or parsing plug-ins;
adding new analysis plug-ins;
writing one-off scripts to automate repetitive tasks in computer forensic analysis or equivalent.