Quantum Espresso

Quantum Espresso is a collection of programs that calculate some properties of crystals. The starting point for most calculations is the program pw.x which calculates the electronic band structure. The basic program has a text input and output. This means you need to create a text file in a specific format that specifies parameters like the Bravais lattice, the atomic positions, and the precision to which the calcuation is performed. This input file is passed to to the program which then produces a text output file that contains the band structure. This output file can be used by other programs to plot the band structure or to calculate the electronic density of states. The output of pw.x can also be given to a program that will calculate the forces between the atoms. The output of that program can passed to another program that will calculate the phonon dispersion relations.

Installation
Purists can download Quantum Espresso from GitHub. On may Linux distributions, Quantum Espresso can be installed with a command like, 'sudo apt-get install quantum-espresso'. Binaries for Windows and MacOS are available. See the Quantum Espresso downloads page. There are also GUIs like BURAI and Winmostar which relieve you from having to create text files.

Example calculations

Cr bcc - using Winmostar
Cu - using BURAI
Cu - detailed description (pdf)
GaAs
GaN
GaP
Ge
InAs
6H SiC
V bcc - using Winmostar

Quantum Espresso website
Quantum Espresso on Wikipedia
BURAI - a GUI for Quantum Espresso
Winmostar - a GUI for quantum chemistry (MOPAC, CNDO/2, GAMESS) molecular dynamics (LAMMPS, Amber), and solid state physics (Quantum Espresso, OpenMX, FDMNES) calculations.