NAND :- Molecular simulation
NMRNotebook :- NMR analysis
NWChem :- High performance comp chem
NMRPipe :-NMR analysis
NMRViewJ :-NMR analysis
nuccyl :-PyMOL helper
Numerical Tools :-Binaries for a range of packages
O :- crystallographic modeling tool
OpenBabel :- Chemoinformatics
OMEGA :- Conformational analysis
OnScreen DNA :- DNA visulisation
OpenDX :-Data analysis
OpenMM:- MM Library
OpenMM is a library which provides tools for modern molecular modeling simulation. As a library it can be hooked into any code, allowing that code to do molecular modeling with minimal extra coding. Moreover, OpenMM has a strong emphasis on hardware acceleration, thus providing not just a consistent API, but much greater performance than what one could get from just about any other code available.
M. S. Friedrichs, P. Eastman, V. Vaidyanathan, M. Houston, S. LeGrand, A. L. Beberg, D. L. Ensign, C. M. Bruns, V. S. Pande. “Accelerating Molecular Dynamic Simulation on Graphics Processing Units.” J. Comp. Chem., (2009), 30(6):864-872, available at: http://www3.interscience.wiley.com/journal/121677402/abstract
ORCA:- General purpose tool for quantum chemistry
ORCA is a flexible, efficient and easy-to-use general purpose tool for quantum chemistry with specific emphasis on spectroscopic properties of open-shell molecules. It features a wide variety of standard quantum chemical methods ranging from semiempirical methods to DFT to single- and multireference correlated ab initio methods. It can also treat environmental and relativistic effects. Due to the user-friendly style, ORCA is considered to be a helpful tool not only for computational chemists, but also for chemists, physicists and biologists that are interested in developing the full information content of their experimental data with help of calculations.
OSRA:- Optical Structure Recognition
OSRA is a utility designed to convert graphical representations of chemical structures, as they appear in journal articles, patent documents, textbooks, trade magazines etc., into SMILES (Simplified Molecular Input Line Entry Specification - see http://en.wikipedia.org/wiki/SMILES) or SD file - a computer recognizable molecular structure format. OSRA can read a document in any of the over 90 graphical formats parseable by ImageMagick.
Partek :- Data analysis
PC GAMESS/Firefly :- Computational Chemistry package

List of some key features:
Free and fast! Proven reliability and performance of Windows/Linux PC GAMESS/Firefly.
Feature rich - supports all the functionality of Windows/Linux-based PC GAMESS/Firefly.
Runs on Mac OS X 10.4.x (Tiger) and 10.5.x (Leopard).
Parallel jobs run on SMP/multi-core hardware without additional software.
Installation is straightforward with a native DMG installer. New drag and drop job submission applications make running jobs significantly easier and more intuitive than most other ab-initio computational chemistry programs on the Mac platform. Just drag and drop your input file on to the appropriate run application for the number of CPU cores desired (or double-click and select) and your job will simply launch and open the output in a suitable text editor. All the necessary output files that may be needed for future follow-up jobs are automatically delivered to the input file directory. Everything is intended to be Mac friendly including a set of Mac-specific step by step Quick Start and Complete install and usage guides that should cover 90%+ of all potential questions for new users.
A batch job submission application and a STOP-FIREFLY-JOBS application which allows multiple job management.
A good set of third-party Mac native graphical applications is available to prepare input jobs as well as to visualize the output of those runs (e.g., WebMO). Most visualization tools that are not available natively for Mac work fine through Darwine or Crossover Wine.
There is an active community of Mac beta testers and Firefly community users to answer questions for new users.
PCModel :-Molecular modelling
Peacock :- Mass spec tool
Here is a quick overview of what you can do with Peacock.
- Read NetCDF GC/MS files
- Identify peaks in chromatograms
- Identify compounds associated with peaks
- Make a summary of all your analyses
Periodic Table
PerlMol :- Chemoinformatics
PFAAT :-Sequence alignment
Polyxmass :- Mass Spec analysis
Pooch :- Cluster computing on Mac
PMV :-Molecule viewer
proFit :-Data analysis
Protein Dynamics :- Molecular simulations
PSI3:- Quantum Chemistry
- Arbitrarily high angular momentum levels in integrals and derivative integrals. (Up to m-type functions have been tested.)
- Coupled cluster methods including CC2, CCSD, CCSD(T), and CC3 with RHF, ROHF, UHF, and Brueckner orbitals.
- Determinant-based CI including CASSCF, RAS-CI, and Full CI.
- Multithreaded integral-direct SCF, MP2, and MP2-R12.
- Excited state methods: CIS, CIS(D), RPA, EOM-CCSD, and CC3.
- Analytic energy gradients for CCSD with RHF, ROHF, and UHF orbitals.
- Coupled cluster linear response methods for static and dynamic polarizabilities and optical rotation.
- Diagonal Born-Oppenheimer correction (DBOC) for RHF, ROHF, UHF, and CI wave functions.
PSILO :- Macomolecular Database
PyMOL :-Molecule viewer
If you would like to enable the use of plugins in PyMol read this tutorial here