What are some alternatives?
When comparing Andy's FLV Joiner and MKVExtractGUI, you can also consider the following products
MP4Joiner - MP4Joiner is a multi-functional and cross platform application for joining the multiple MP4 music clips.
FFmpeg - Open source multimedia suite for conversion, playback, profiling, and streaming.
MKVToolnix - MKVToolnix is a set of tools to create, alter and inspect Matroska files under Linux, other Unices...
gMKVExtractGUI - GUI front-end for mkvinfo and mkvextract CLI tools.
Boilsoft Video Joiner - Boilsoft Video Joiner is a powerful video merger to join AVI, MPEG, MPG, VOB, RM/RMVB, 3GP, ASF, WMV, WMA, MP4, MP4A, MKV or FLV files, and so forth.
Subler - Subler is a Mac OS X application that opens media containers, allows you to add or remove media...