Aeyae Remux can be used to extract portions of original video into a separate file. Aeyae Remux is a GOP-based editor (GOP = Group Of Pictures), which means it doesn't do any transcoding, only remuxing. However, it can truncate a GOP.
Aeyae Remux can be used to stitch together files... within reason. Since it is only a remuxer -- stitched files must be of compatible format. This means stitched files must have the same audio/video codecs, and codec properties (width, height, sample rate...