Latest release:  spfirst_v175.zip   (Feb, 2024)
Available for all versions of MATLAB back to 7.2 (2006):

Install:

Add these files to MATLAB and update MATLAB's path:

1. Download the ZIP file that contains everything. It is called spfirst_vNNN.zip.
2. Unzip spfirst_vNNN.zip somewhere. A good choice would be the directory: ...\MATLAB\toolbox\spfirst\.
   The unzip will create a bunch of subdirectories.
   NOTE: use forward slash for directories on Mac or Linux.
3. Then add this one directory ...\MATLAB\toolbox\spfirst\ to the MATLAB path.
   This can be done in MATLAB from the Home Tab ➤ Environment ➤ Set Path.
   
   NOTE: For versions previous to R2012a, select from menu File ➤ Set Path.
4. Next, type the command spfirst at the MATLAB comand prompt.
   It will add the other appropriate subdirectories to the path.
5. Finally, under Home Tab ➤ Environment ➤ Set Path, do a save of the new path.

Once the MATLABPATH is correct, you should be able to type zdrill or sindrill at the MATLAB command prompt and have a GUI start up.
Also, commands like zprint will now work.

Uninstall:

Delete all the files and directories in ...\MATLAB\toolbox\spfirst\
and also manually remove the directories from MATLAB's path via Home Tab ➤ Environment ➤ Set Path.