ANTLR 2 (http://www.antlr2.org/license.html) :

ANTLR 2 License

We reserve no legal rights to the ANTLR--it is fully in the public domain. An 
individual or company may do whatever they wish with source code distributed 
with ANTLR or the code generated by ANTLR, including the incorporation of ANTLR, 
or its output, into commerical software.

We encourage users to develop software with ANTLR. However, we do ask that 
credit is given to us for developing ANTLR. By "credit", we mean that if you 
use ANTLR or incorporate any source code into one of your programs (commercial 
product, research project, or otherwise) that you acknowledge this fact 
somewhere in the documentation, research report, etc... If you like ANTLR and 
have developed a nice tool with the output, please mention that you developed it 
using ANTLR. In addition, we ask that the headers remain intact in our source 
code. As long as these guidelines are kept, we expect to continue enhancing this 
system and expect to make other tools available as they are completed.