What are some alternatives?
When comparing MKVToolnix and Subler, you can also consider the following products
FFmpeg - Open source multimedia suite for conversion, playback, profiling, and streaming.
MP4Joiner - MP4Joiner is a multi-functional and cross platform application for joining the multiple MP4 music clips.
MKVExtractGUI - This is a GUI frontend for mkvextract from ...
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.
gMKVExtractGUI - GUI front-end for mkvinfo and mkvextract CLI tools.
HandBrake - HandBrake allows users to easily convert video files into a wide variety of different formats.