The source can be downloaded here
  https://github.com/neurolabusc/NiiStat
Github is owned by Microsoft, so it is pretty well maintained and should work with most browsers.

If you have a Mac or Linux, I would install the git command line tools. This will allow automatic updates. In this case, you can install NiiStat with a single command from your terminal:
  git clone https://github.com/neurolabusc/NiiStat.g...
next, you just need to install the 'NiiStat' folder in your Matlab path.

For studies with only a single modality (e.g. all images are lesions) you can run the command 'nii_nii2mat' from Matlab to convert all your NIfTI images to the Matlab structure NiiStat uses. You can then try out the Wiki for more details
  https://www.nitrc.org/plugins/mwiki/index.php/niistat:MainPage

NiiStat includes a lot of nice features for multiple modalities, machine learning, etc. However, you will get similar results for traditional multivariate analyses using other tools. You may want to explore if you find those other tools simpler to use. The flexibility of NiiStat can make it a bit overwhelming for simple studies. I would suggest you look at

VLSM http://aphasialab.org/vlsm

PALM https://github.com/andersonwinkler/PALM