Stellarium is the foremost tool for archaeoastronomical visualisations. It not only generates sky visualisations for any place and time but incorporates tools for integrating 3D models of architecture embedded in their surrounding landscape. It is open source.
Horizon visualization from DTM data
Andrew Smith’s “HORIZON” tool generates visualisations of horizon profiles annotated with azimuth, altitude and declination and showing rising and setting paths of the sun, moon and/or selected stars as desired.
This basic declination calculator calculates the astronomical declination of any structural alignment given the true azimuth, horizon altitude, and terrestrial latitude. It applies a mean refraction correction to the observed altitude and (for geocentric lunar declinations) mean lunar parallax.
It is an interactive version of the “GETDEC” program referred to in Astronomy in Prehistoric Britain and Ireland (p. 169) with only the basic functionality included (i.e. no offsets etc.).
Older programs mentioned in Astronomy in Prehistoric Britain and Ireland, such as the original GETDEC program, are no longer available. Most are long obsolete. For example, GRIDLA and LAGRID have been superseded by several tools available on the web, such as (for the British National Grid) the Ordnance Survey’s Coordinate tools.