FASILL runs over SWI-Prolog. You can download the latest version of SWI-Prolog here.
Download or clone the FASILL repository: git clone https://github.com/jariazavalverde/fasill.git
Enter the fasill folder: cd fasill
Execute the install.sh bash script: sudo ./install.sh
That's all! Now you can run FASILL by typing fasill in your terminal: fasill