The Spartan Graphical User Interface. Spartan has a single, fully-featured GUI that many consider to be the best in the business. In very little time, you can build and manipulate molecules, run molecular mechanics and quantum chemical calculations, display your results in graphical form and address your chemistry.
Builders and More:  
Accesses a builder for common organic fragments (e.g., "sp3 carbon"), functional groups and rings for easy construction of organic molecules.
  Expert Extends building throughout the entire Periodic Table. Includes groups, rings and a library of common ligands.
  Peptide Accesses a library of amino acids for construction of polypeptides as helices, b sheets or in user-defined conformations.
  Nucleotide Accesses a library of nucleotide bases for construction of single or double stranded DNA or RNA as helices or in user-defined conformations.
  Transition States Provides guess for transition states by pattern matching to an extensive library of precalculated structures. The user needs only to specify reactant(s) and "reaction arrows". The "fallback" is the linear synchronous transit method.
  Library Accesses a user-defined library of structures to initiate building.
  Substitution Facilitates construction of related sets of molecules by substituting a "parent" molecule.
  Cambridge Structural
Accesses the Cambridge Structural Database (CSD)* of >225K experimental X-ray crystal structures for organic and organometallic molecules, together with their literature references. Optionally adds hydrogens and refines hydrogen positions.

* CSD needs to be licensed from the Cambridge Crystallographic Data Centre or one of its distributors.
  Structural Refinement Allows fast minimization inside the builders using either SYBYL or MMFF94 molecular mechanics.