What are the conditions to use FEniCS in an industrial application? For instance, can FEniCS be used in similar terms to COMSOL? If so, are there any conditions like releasing the code used in the application?
Most of FEniCS is released under the Lesser GNU Public License, version 3 (LGPL, https://www.gnu.org/licenses/lgpl-3.0.en.html). This permits commercial use. It does place some requirements on releasing modified FEniCS code if you distribute code/binaries. The 'L' in LGPL means that you can link to FEniCS without that affecting the license of your own code.