Free open source graphical user interface (GUI) for molecular modelling, written in Python and distributed with source code, a bundled executable, well documented API, a user manual and built-in tutorials. FU has a rich functionality for biochemical applications, and users familiar with Python can easily modify existing features. Pyshell allows interactive Python commands and scripting. BSD 2 license makes it possible to use the modified code freely. FU can make input file for GAMESS calculations, and has an extensive support of FMO, for making input files and visualizing results.