FEM Install

Introduction
To be able to do a Finite Element Analysis (FEA) using the FEM Worbench FreeCAD makes use of two external programms. One is used for generating the FEM-Mesh and the other for solving the system of equations.

FEM Solver
For solving the system of equations CalculiX is used. See http://www.calculix.de/ FreeCAD writes an CalculiX input file starts CalculiX and reads the output of CalculiX. It means CalculiX binary is standalone and independent from FreeCAD. Because of this and since there are more possibilities to get a valid FEM-Mesh it is recommended to install the Solver first. Up To date (mid 2015) CalculiX is the only supported Solver of the FEM module.

FEM Mesh Generator
As meshing tool to create a FEM-Mesh netgen is used. See https://sourceforge.net/projects/netgen-mesher/ To use Netgen in FEM module FreeCAD needs to be compiled against netgen libraries. There are other possibilities to create an FEM-Mesh in FreeCAD too. Check out the FEM-Mesh Wiki page(ToDo).

Windwos
If either a stable or development version from Download is used no further software needs to be installed. Netgen and CalculiX are included in the FreeCAD download package.

Ubuntu PPA
The easiest possibility to get an working FEM Workbench on Linux is the use of the Ubuntu PPA Version. Check out Download. The netgen FEM Mesh Generator is allready included in the ppa version. CalculiX is an extra package provided by the Ubuntu PPA Version as well. If the Ubuntu PPA repository is allready added to your package manager install CalculiX by apt-get install ccx

The following FreeCAD Ubuntu PPA packages have Netgen and CalculiX:
 * Ubuntu 14.04 (Trusty Tahr)
 * Ubuntu 14.10 (Utopic Unicorn)
 * Ubuntu 15.04 (Vivid Vervet)

For Developers: There is a huge forum thread in which the creation of the Ubuntu PPA packages was disscussed. It may be usefull if the Ubuntu PPA packages needs to be updated.

Other
On other Linux distributions you need to make sure to get the appropriate software and libraries installed yourself before using FEM workbench.

CalculiX
Since CalculiX is a standalone software you either can install a CalculiX binary or compile CalculiX yourself. Any CalculiX version from 2.7.X works with FreeCAD. Since there hasn't been much changes in CalculiX resently lower versions than 2.7.X might work as well.

Install CalculiX Binary
There are only a few Linux Distributions which are known to have CalculiX Packages in their Repositories. Following a list:
 * Arch Linux --> https://aur.archlinux.org/packages/calculix/

On the CalculiX Website it is possible to download a generic Linux binary of CalculiX. Check out http://www.dhondt.de/ Since any Linux Distribution could have different library paths it is likely possible this binary will not work out of the box at your linux distribution. Check out the following FreeCAD forum threads for more infomation:
 * Fedora 21 --> http://forum.freecadweb.org/viewtopic.php?f=18&t=10140
 * Some bash commands that may help --> http://forum.freecadweb.org/viewtopic.php?f=3&t=11830&start=20#p95741

Compile CalculiX
Compiling CalculiX is not as easy as it is with many OpenSource software. There are many different resources at FreeCAD forum and the internet. Check out the following:
 * Debian --> http://forum.freecadweb.org/viewtopic.php?f=4&t=5975&start=10
 * There is a CMake Repository on github, but at FreeCAD forum noone has reported if this one works
 * https://github.com/ricortiz/CalculiX-cmake

Netgen

 * ToDo

Further Informations
The FreeCAD forum is a very good resource for informations in this regard. Check out google search on FreeCAD forum page by :
 * [ https://www.google.ch/search?q=sys.append.path+site%3Aforum.freecadweb.org#q=calculix+site:forum.freecadweb.org calculix site:forum.freecadweb.org]
 * [ https://www.google.ch/search?q=sys.append.path+site%3Aforum.freecadweb.org#q=netgen+site:forum.freecadweb.org netgen site:forum.freecadweb.org ]

OSX
Neither Netgen nor CalculiX are included in FreeCAD download packages which can be downloaded from Download

CalculiX
Check out the following forum thread.

Netgen
There is no known documantion source for FreeCAD and netgen on OSX. Check out FEM Mesh wiki (ToDo) for other possibilities to create a FEM Mesh.