Source: https://github.com/jeromerobert/pdfarranger
pdfarranger is a small but helpful tool that lets you split, merge and rotate pdf documents in an easy way. It has a clean an minimal ui so that almost everyone is able to use that tool.
There is no comparable tool in the repo that lets you do that that easily. The more advanced pdf editors are too complicated and not good in that particular task, as there is not such an easy gui