Freeware Descriptions:
Avogadro is an advanced molecular editor designed for cross-platform use in computational chemistry, molecular modeling, bioinformatics, materials science, and related areas. It offers a flexible rendering framework and a powerful plugin architecture.
Here is complete features (taken from authors site):

File Size / OS:
- 7.88 MB / Windows 9x - ME - 2000 - NT - XP - 2003 - Vista
Download Avogadro 0.9.1: