qmol is a simple molecular weight calculator, available for Linux and Windows, derived from Tomislav Gountchev's KMol. You can enter a formula, (e.g. CH3(CH2)2OH) and get its molecular weight (60.0959 g/mol) and its elemental composition (C3H8O: C 59.96; H 13.42; O 26.62 %).
- Pre-defined groups (alkyls/aryls, amino acids)
- User-defined groups
- Protein/oligopeptide calculation mode
- One-letter amino acids parsing in square brackets 
- History of recently calculated formulas
- Configurable output
- Command line calculation