Seattle filmworks distibutes "free" film if you use their mail-in processing services. They used to give away old/recycled movie internegative film that you couldn't have developed at most labs. If the underside is black and/or the sprockets are more rounded than usual, this is probably whar you have. In recent years they have switched to film that uses standard C41 processing. As to who makes it... I have no idea. The rolls I have seen had no brand printed on the sprocket area like name-brand film.
Both Agfa and Ferrania have large store brand film operations. Agfa supplies Polaroid with their C41 35mm film, as well as Food Lion and many others. I believe Ferrania produces film for Walgreens (but I might have this mixed up).
Seattle Film Works, now Photoworks (go to photoworks.com), film is made in Italy. That would lead one to suspect Ferrania. They do not advertise their chrome film, but my father was able to get it despite it not being offered on their public sites. He shot his last role of it in 1999 just a few months before he died. The color and quality of the slides was pretty good. I used one roll that he had left over. Never tried to get any more of it.
Photoworks has always offered slides or prints or both from their print film. When you order the slides you get some very interesting colors, and they are very difficult to scan. I used to use their film, but have not done so in years, although I have recently gotten some very good prints from them of digital files.