<unk>  is a computer program written for molecular graphics visualization intended and used primarily for the depiction and exploration of biological macromolecule structures, such as those found in the Protein Data Bank.  It was originally developed by Roger Sayle in the early 90s.
Historically, it was an important tool for molecular biologists since the extremely optimized program allowed the software to run on (then) modestly powerful personal computers. Before<unk> , visualization software ran on graphics workstations that, due to their expense, were less accessible to scholars.<unk>  has become an important educational tool as well as continuing to be an important tool for research in structural biology.<unk>  has a complex version history. Starting with the series of 2.7 versions,<unk>  is licensed under a dual license (GPL or custom license RASLIC). Thus,<unk>  is (along with Molekel, Jmol and PyMOL), among the few open source molecular visualization programs available.<unk>  includes a language (for selecting certain protein chains, or changing colors etc). Jmol has incorporated the<unk>  scripting language into its commands.
Protein Databank (PDB) files can be downloaded for visualization from the Research Collaboratory for Structural Bioinformatics (RCSB) bank. These have been uploaded by researchers who have characterized the structure of molecules usually by X-ray crystallography or NMR spectroscopy.
RasMol
Entrez
AEMT-CC
TNM
MoCA
BRAF
APC 
G-LOC