There is Wirth and Gutknecht's Oberon System. It's still available but is older than Visopsys -- it was created around 1990, then updated in 2013. I think

There is Wirth and Gutknecht's Oberon System. It's still available but is older than Visopsys -- it was created around 1990, then updated in 2013. I think it's now considered an historical artifact. https://www.projectoberon.net/ https://www.projectoberon.net/