This is Personal Package Archive (PPA) for MindForger.
To install programs from this PPA add new repository
to /etc/apt/sources.list as follows:
echo "deb http://www.mindforger.com/debian-ppa/stretch stretch main" | sudo tee /etc/apt/sources.list.d/mindforger.list
... and import key that is used to sign the release:
$ wget -qO - http://www.mindforger.com/gpgpubkey.txt | sudo apt-key add -
After that you can install MindForger as any other software package:
$ sudo apt update
$ sudo apt install mindforger