XCrySDen is a crystalline and molecular structure visualization program, which aims at display of iso surfaces and contours, which can be superimposed on crystalline structures and interactively rotated and manipulated.
http://www.xcrysden.org/
![](http://www.xcrysden.org/img/xcrysden-in-action-200.png)
![](http://www.xcrysden.org/img/xcrysden_molsurf2-200.png)
http://www.xcrysden.org/