I have no idea! I don't know what the situation has been up to now, I guess the OSX version has been compiled on a machine with those drivers for the last few years at least, since if I understand correctly that is the only way to support these devices.
source: http://spacenav.sourceforge.net/All parts of the spacenav project are written and maintained by John Tsiombikas (email@example.com), and released as free software.
The spacenavd driver is released under the GNU General Public License (GPL) version 3 (or any later version). This means that you can run it without any restrictions, for any purpose, you can modify it, and you can re-distribute it verbatim or with any modifications. However, if you release anything that contains this code or parts of it, you must release it under the terms of the GPL v3 (or at your option, any later version published by the free software foundation). For more details, see the full text of the license.
The libspnav library, is released under the terms of the "modified" (3-clause) BSD license. This means that you can use it without any restrictions, you can modify it, and re-distribute it verbatim or with any modifications, under any license. However, you must retain the copyright notices in any source files containing code from the library, and binary redistributions must include the copyright notice in any documentation or other acompanying materials. For more details, see the full text of the license.
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Then I guess we should add libspnav to conda-forge. Shouldn't be too much trouble for linux/osx. Not sure about windows.
Really, until now I didn't know about it at all.
For FreeCAD at least the library isn't needed for Win. FreeCAD's support uses Windows native events.