Astronomy Software
Web

Aladin lite is a lightweight version of the Aladin Sky Atlas, running in the browser and geared towards simple visualization of a sky region.
Aladin lite is powered by the HTML5 canvas technology, currently supported by any modern browser. Aladin lite is easily embeddable on any web page and can also be controlled through a Javacript API.

Explore the world in 3D. The application lets you zoom in any part of the world.
Explore the Earth, but also the sky, the Moon and Mars.

It offers a photographic map of several regions of the moon with zooming capability. Google Moon also shows you the locations and provides detailed descriptions of each of the 6 Apollo landings on the moon.
The data which Google Moon uses to create the elevation layers comes from the U.S. Geological Survey.

A Web-based computer program for calculating the regional environmental consequences of a meteoroid impact on Earth. Great data and a useful tool.
The most awesome asteroid impact calculator on the Web!

It enables your computer to function as a virtual telescope, bringing together imagery from the best ground and space-based telescopes in the world.
Experience narrated guided tours from astronomers and educators featuring interesting places in the sky.

World Wind allows any user to zoom from satellite altitude into any place on Earth, leveraging high resolution LandSat imagery and SRTM elevation data to experience Earth in visually rich 3D, just as if they were really there.
Particular focus was put into the ease of usability so people of all ages can enjoy World Wind. All one needs to control World Wind is a two button mouse. Additional guides and features can be accessed though a simplified menu. Navigation is automated with single clicks of a mouse as well as the ability to type in any location and automatically zoom into it.

Sky-Map.org (or WikiSky.org) is a wiki and interactive sky map that covers more than half a billion celestial objects. Users can view the whole star sky at once and zoom in to view areas in greater detail. WikiSky includes many stars, galaxies, constellations, and planets, but it is still in development. Users can also edit information about different stars by writing articles, adding Internet links, uploading images, or create a special interest group for a specific task.

Stellarium Web is an online planetarium running in your web browser based on the open source stellarium web project.
It shows a realistic sky in 3D, just like what you see with the naked eye, binoculars or a telescope.
Just set your coordinates and go.