Prerequisites

Python
wxPython
SciPy
CCP4 and Phenix
Matplotlib
Clipper libraries

Crystallographic software is not strictly necessary (for example, if Phenix is missing on your system, ShakErr will run fine until you try running jobs with phenix refinement). In theory, you only need to configure ShakErr to find refmac5, cif2mtz, uniquiefy and phenix.refine in "Software" tab of the main window. The warning dialog when you start will still appear though (it looks for CCP4_MASTER environmental variable).

Clipper libraries are only needed for model error estimates in reciprocal space.

For Ubuntu/Debian users, the following should work to get wxPython and scipy (you have python installed by default, see CCP4 and Phenix pages for specific installation instruction of the crystallography packages):
sudo apt-get install python-wxgtk2.8
sudo apt-get install python-scipy
sudo apt-get install python-matplotlib
sudo apt-get install libclipper2

Download ShakErr

The latest version is available here. Notice that beginning with version 0.2.25, the 32-bit and 64-bit versions are available, which refers to the shaclip executable.

Linux

Create temporary folder, move the downloaded tarball into it, untar and change to the newly created folder, e.g.
mkdir tmp
cd tmp
mv ~/Downloads/shakerr-0.2.8-Bartoszyce.tar.gz .
tar xvzf shakerr-0.2.8-Bartoszyce.tar.gz
cd shakerr-0.2.8-Bartoszyce
Now build the package for your distro.
./setup.py build
The installation itself requires admin privileges. Specific commands depend on Linux distro as well as your personal preferences. You can always just switch to root account. In Ubuntu
sudo ./setup.py install
And to clean up
cd ../../
rm -fr tmp
This is it! Just type "shakerr" in the command line and hit enter.

Install without admin privileges

If you don't have administrative privileges, donwload the "notroot" tarball (e.g. shakerr-0.2.5-Barczewo-notroot.tar.gz). Untar it as above somewhere, this will create the same folder. However, it will not contain the setup.py script, but the "shakerr" executable instead. Just change working directory to that folder and execute it. Alternatively, you can create an alias, e.g. add this to your ~/.bashrc file
alias shakerr='/home/sware/shakerr-0.2.8-bartoszyce/shakerr'
Of course, the disadvantage here is that shakerr will not become automatically available to other users of the workstation until they set up the same alias. And the caveat remains that you have to have all the prerequisites, but you only need to ask your system administrator to install it and then you can keep updating ShakErr on your own.

Mac OSX

The above Linux installation procedure should work.

Microsoft Windows

There is currently no Windows installer. It's not hard to make, but it failed to run the last time I tried. I'll look into it at some point, but it's obviously low priority.