Online Calculators (all free)

Conversion of properties:
Conversion Factors

- including energy, H, S, Cp, P, V and T; Process Associates of America.
megaConverter

- claims to be the Web's (and the Universe's) best place to figure what equals what; Ben-Cam InterMedia.
Measurement Conversion Calculator

- ConverIt.com, Inc, Las Vegas, NV, USA.
Temperature Conversion Calculator

- College of Chemistry, UC Berkeley, CA, USA.
 
Chemical Reaction:  
Reaction-Web

- F*A*C*T online H, S, G, V, Cp properties calculation for a species or chemical reaction; CRCT École Polytechnique, Montréal, Québec, Canada.
 
Chemical and Phase equilibria:
Aqualib-Web

- FactSage online chemical equilibria of a dilute aqueous solution with an ideal gas and pure solids at 298.15 K; CRCT École Polytechnique, Montréal, Québec, Canada.
Equilib-Web

- FactSage online chemical equilibria of an ideal gas with pure solids and liquids; CRCT École Polytechnique, Montréal, Québec, Canada.
Predom-Web

- FactSage isothermal predominance area diagram (one metal); CRCT École Polytechnique, Montréal, Québec, Canada.
EpH-Web

- FactSage Eh vs Pourbaix diagram (one metal); CRCT École Polytechnique, Montréal, Québec, Canada.
Geology

- links to online thermodynamics and phase equilibrium calculations in geology such as WEBINVEQ for performing thermobarometry calculations; Terry Gordon, University of Calgary, Alberta, Canada.
 
Miscellaneous:
Chemical Calculations

- including Molecular Weight, Molecular Formula, Synthesis Calculator, Boiling Point; Magnus Program, Department of Chemistry, Cambridge University, UK.
Gaseous Equation of State Calculator

- taken from Monachos Engineering; Thessaloniki , Hellas (Greece).
Gas Law Calculations and over 8,000 other calculators

- from Calculators On-Line Center; Jim Martindale, Newport Beach, CA, USA.
TEST

- extremely useful multi-purpose thermodynamic problem solver featuring: visual calculator, thermodynamic plots, what-if scenarios, spreadsheets, exergy analysis, various miking systems, combustion, cycles, and more; Sybrata Bhattacharjee, San Diego State University, USA.