Just found this library a couple days ago. Finally there's a working ADE replacement for Linux.
Though, I found two slight bugs in acsmdownloader. The first one is when I try to export the private key to a particular file like this: "acsmdownloader -d device.xml -a activation.xml -k devicesalt -o output.der -e" Then I get the following error:
Exception code : 0x1004
Message : Unable to open
When I leave out the "-o output.der" then everything works.
The 2nd bug is a typo in the help output "Usage:" line. That one says the short form for "--device-key-file" would be "-s" but according to the help (and the source code) it seems to be "-k" instead.
Also, not sure if people would be interested in that, but I decided to create a Calibre plugin that includes libgourou so that you can configure your ADE account in the Calibre settings and just drag-and-drop your ACSM file into Calibre. If you're interested in that, here it is:
https://github.com/Leseratte10/acsm-calibre-plugin
Though that plugin is for Linux only. Did you ever test compiling libgourou for Windows or for Mac? It'd be cool to have support for Windows and Mac in that plugin, too, so Windows users wouldn't need ADE either, but I don't know enough C++ to figure out why that fails.