Calistry.org is described as «Calistry is an online Chemistry Calculator. Till date Calistry contains 70+ calculators in the field of Chemistry. Everything in the website is entirely free to use» and is a Calculator in the education & reference category. There are more than 10 alternatives to Calistry.org for a variety of platforms, including Mac, Windows, Linux, iPad and Online / Web-based. The best alternative is Wolfram Alpha, which is free. Other great apps like Calistry.org are Avogadro, Jmol, Rasmol and Unit Converter Tool.
