I recommend OpenCMIS. (Well, I have to since I participate in the project.) This is an active project supported by the wider community. OpenCMIS supports both bindings, AtomPub, and web services, and has been tested against several repositories.
chemistry-atompub-client was left, and chemistry-abdera is not very active. Of course, you can directly bind to the AtomPub binding, but that works a lot.
Florian mΓΌller
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