online external ballistics software x-ballistics
x-ballistics is a free online external ballistics programm.
no installation required, it runs in a browser, just click this 
link.
- no need to know the muzzle velocity, simply can calculate from 2 points of impact
- trajectory
- sight settings
- 3-DOF for bullets
- 6-DOF for arrows
- metric and imperial units
- multilanguage: english and german
- editor for reticle
Use at your own risk!
To store data, a registration is required.
Registered user can save your data.
The sourcecode of x-ballistics is under GPLv3.
Ballistic Software Arrowmatcher
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.
Links
Ballistic applications and know-how not only for crossbow archers:
- www.texasarchery.org/L1/ArcheryLinks.htm
big linklist mainly for archers. - www.loadammo.com/Topics/September01.htm
description of the ballistic coefficient. - www.snipercountry.com/ballistics/
Programs (u.a. smallball) and tables (G1,G2 ..). - www.smoothey.org/mse.pdf
very interesting for programmers. (PDF-Document). - www.nennstiel-ruprecht.de/bullfly/
external ballistic - www.arrowinapple.de
look at "Armbrust-Vergleich" this is a very good comparison of some crossbows. This is a german site, but for the comparison, there is also a english version offered. - http://linux.softpedia.com/get/Science-and-Engineering/Mathematics/Small-Arms-Ballistics-2908.shtml
Simple ballistic program for linux. It calculate the trajectory and the Ballistic Coefficient of a bullet. It is possible to switch the Unit System in english or metric system. This is also useable for crossbows. - http://www.thecrossbowmansden.com/Home.html
good site about building of crossbows 
www.tap46home.plus.com/mechanics/
english Website with good infos about wind drift, and much more,
look at Downloads->Arrow comparison program