LogMerger is a free program that let you merge any number of logfiles into a single file and still maintain the same chronological order.
This is useful if you’ve got a website with more than one front-end or a cluster solution with more than one web server for load-balancing reasons, and thus you’ve got more than one logfile for the same period of time. Most log analyzes programs only accept a single logfile, so in order to get statistics you must merge the different logfiles into one. However, it’s not just a simple matter of concatenating them together, because they still need to maintain their chronological order.

That is exactly what LogMerger does, depending on the timestamp in the logfiles, it merges the files together and still maintain the same chronological order through out the whole file.