I recently acquired piece of hardware I had never heard of before: a SuperBox II unit. These were used in laserdisc kiosks to control industrial players via the serial port on the back. The most astonishing thing is http://www.superbox.com/ is still online and all of the software and documentation has been preserved.

The AC adapter was included as well as the cable that goes to the laserdisc player, but I'll have to make my own user input device consisting of buttons.

Has anyone ever heard of this device or know of similar ones?

I don't think I've ever seen an industrial player use an RJ11 connection for communications. I guess these use some weird proprietary cables?

I thought it was RJ11 too when I first saw it, but cable is RJ45 to DB15:
6 -> 1 (GND)
4 -> 2 (TxD)
3 -> 3 (RxD)

Archive the entire website is all I can offer as a suggestion, sorry. I think I've seen a similar device used in pubs, bars and clubs that have karaoke nights.

You rarely see them now but the occasional mobile karaoke night may use one.

Yep I downloaded everything. I even emailed the owner to see if he would be willing to open source the code. That binary is dated 1988!

This disc was included with it https://www.lddb.com/laserdisc/submit/5 ... its-Reel-2