A sane pdf tool to merge/split/rearrange pages

There are so many pdf tools to merge/split/rearrange pages. Most of them are crap, shareware or hardly usable. This one is open source and can even be used to stitch images to a pdf!

It works on linux and windows.

Usually, open source/linux tools are not bullshit, so it is a good advice to not search for "some-tool", but rather for "some-tool open source" or "some-tool linux" (I got this advice from a friend).