Astronomy

Stellarium is opensource (launchpad, github). It comes with a developing “Indian vedic skyculture”, and allows translations with voting (rosetta).

Ephemeris data

DExxx ephemerides from NASA’s JPL

Swiss ephemeris

Swiss Ephemeris is based upon the planetary and lunar ephemeris DE431 developed by NASA’s Jet Propulsion Laboratory, compressed.
Mailing list - swisseph/
Test page - here.
Python wrapper - pyswisseph. git here.

Vedic astrology extensions

M. YANO and M. FUSHIMI here (cached here.)
jagannatha hora - Narasimha rao
mudgala hora - ajit

Python

jyotisha - kArttika.
drik-panchanga well-written Python-based panchangam, with a nice simple GUI

Online services