Maybe LosslessCut: https://github.com/mifi/lossless-cut ? I never used it, but looks promising. HandBrake: https://github.com/HandBrake/HandBrake is also a great GUI tool to convert videos, with some basic editing (cutting and such).
You could also always learn Ffmpeg from commandline and with scripts. Obviously this has a huge learning curve, but once you learn it, you are then free from any GUI or other tool in the future. At least for simple tasks this could be useful when automating. It's on my todo list...