Also uses variational formulation of a partial differential equation like freeFem which is a pain.
One downside is that its documentation is a Springer published PDF https://link.springer.com/content/pdf/10.1007%2F978-3-319-52462-7.pdf which is several years out-of-date (tested with FEnics 2016.2. Newbs. This causes problems e.g.: https://stackoverflow.com/questions/53730427/fenics-did-not-show-figure-nameerror-name-interactive-is-not-defined/57390687#57390687
system of partial differential equations are mentioned at: https://link.springer.com/content/pdf/10.1007%2F978-3-319-52462-7.pdf 3.5 "A system of advection–diffusion–reaction equations". You don't need to manually iterate between the equations.
On Ubuntu 20.04 as per https://fenicsproject.org/download/ Before 2020-06, it was failing with: but they seem to have created the Ubuntu 20.04 package as of 2020-06, so it now worked! https://askubuntu.com/questions/866901/what-can-i-do-if-a-repository-ppa-does-not-have-a-release-file
TODO heat equation hello world.