Apache uses mailing lists.
If you want a forum, well you found it. There are willing people here that can answer ANT and Maven related questions. But ANT has a very decent user manual, I certainly never ran into anything it couldn't answer.
This one seems the most fitting IMO. Third party tool/API questions pop up in several places, including under regular 'java programming'. All new threads are listed under the 'recent threads in this category' here:
anyway so as long as you give your questions a descriptive title people will find it. Just keep in mind that this forum is quite strictly moderated so be sure to read the forum guidelines. Also be aware that people don't like it very much when you spam the same question over several forums either on this site or even forums on other sites (stack overflow, the ranch, etc.); after all you could be spending precious time answering it when it has already been answered somewhere else. When you do you can be sure you will be caught, most regulars here visit or even moderate the popular Java forums.