JNA is dual-licensed under 2 alternative Open Source/Free 
licenses: LGPL 2.1 and Apache License 2.0. (starting with
JNA version 4.0.0). 

What this means is that one can choose either one of these
licenses (for purposes of re-distributing JNA; usually by
including it as one of jars another application or
library uses) by downloading corresponding jar file,
using it, and living happily everafter. 

You may obtain a copy of the LGPL License at:

http://www.gnu.org/licenses/licenses.html

A copy is also included in the downloadable source code package
containing JNA, in file "LGPL2.1", under the same directory
as this file.

You may obtain a copy of the ASL License at:

http://www.apache.org/licenses/

A copy is also included in the downloadable source code package
containing JNA, in file "ASL2.0", under the same directory
as this file.