Arrowmatcher is a ballistic application, released under the GPL. It is for Windows, Mac OS and Linux:
This is a simple tool for mainly crossbowarchers. But it can also used for rifles or other bullets. It can calculate the trajectory of arrows and a little bit more.
Everybody are welcome to post comments at the bottom of each page. Simply click the "new comment" link and a window with the uploadform appear.
Ballistic applications and know-how not only for crossbow archers: