astro does chart arithmetic: where the Sun, Moon and planets are on a given day, a birth chart from a birth date, the slow planets touching it, and numerology. It uses the Swiss Ephemeris by Astrodienst AG.
It is free software under the GNU Affero General Public License, version 3 (the Swiss Ephemeris part is offered under the same licence). If you use it over a network you are entitled to its source: the source of the version running now.
Version 63d07f2, commit 63d07f272b7737bad05ebb52fbb504c22bc4f89d.