What are some alternatives?
When comparing MKVToolnix and MKVExtractGUI, you can also consider the following products
FFmpeg - Open source multimedia suite for conversion, playback, profiling, and streaming.
Subler - Subler is a Mac OS X application that opens media containers, allows you to add or remove media...
gMKVExtractGUI - GUI front-end for mkvinfo and mkvextract CLI tools.
Inviska MKV Extract - Free open-source utility for extracting tracks and other elements from MKV files on Windows, Mac and Linux
HandBrake - HandBrake allows users to easily convert video files into a wide variety of different formats.
MP4Joiner - MP4Joiner is a multi-functional and cross platform application for joining the multiple MP4 music clips.