-> to design/modify the gnusb hardware
The EAGLE Layout Editor is an easy to use, yet powerful tool for designing printed circuit boards (PCBs). The name EAGLE is an acronym, which stands for Easily Applicable Graphical Layout Editor
On Ubuntu you should use the Synaptic Package Manager to install eagle. The downloaded package doesn't seem to install on ubuntu....
While installing, eagle will open to let you choose your license. Select "Freeware License" and exit eagle to finish the installation process.
You might follow more or less these instructions
The libusb library allows user space applications to access any USB device on Windows in a generic way without writing any line of kernel driver code.
Libusb is probably already installed on your linux distribution. However, to program your own drivers you'll need also the library development files: libusb-dev.
On ubuntu linux, select libusb-dev in the Synaptic Package Manager.