2DTiler
2dTiler an interactive viewer for periodic tilings of all three twodimensional geometries
2dTiler is an interactive viewer for periodic tilings of all three twodimensional geometries, written by Daniel Huson and Klaus Westphal.
Input is a file of records, each describing a DelaneyDress symbol, a datastructure that prescribes the topology and symmetries of a periodic tiling, and output is the picture of that tiling. The geometric shape of the tiles and the specific symmetry group can be interactively modified.

Binaries for linux can be downloaded here.

Binaries for Mac OS X (10.5) on intel can be downloaded here.
Note that since 10.10 (Yosemite) the directory /usr/X11 is now /opt/X11. To get 2dt to run, please type the following command:
sudo ln s /opt/X11 /usr/X11

Binaries for windows may be provided in the future.
See also: RepTiles, a 2dtiling program for Classic Macs.