qmol is a simple molecular weight calculator. 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 %). You can define your own custom group symbols, provided they do not interfere with an element's name.

It is a major rewrite of Tomislav Gountchev's kmol. I really enjoyed using kmol for daily laboratory use in synthetic inorganic chemistry. My original intention was to port kmol, which was based on kde3 libraries, to kde4, to get rid of the old kde3 dependencies. But at the time I tried that, I did not understand enough of C++/Qt to be able to do it. So I decided I'd analyze the code by coding the application more or less from scratch without the kde dependencies (i.e. pure Qt) using qtcreator.