Bifrost is or was a very small Linux distribution designed for infrastructure networking, routers and firewalls. It was designed to be very simple (KISS).
Swedish involvement indicated
The Resilans AB corporation is or was heavily involved with the Bifrost distribution. This corporation still exists. However, their home page for the distribution, bifrost.slu.se, is no longer functioning. Thus, they either decided to close it up and no longer share the code or they abandoned it and moved on. We do not know what happens to be the case. Resilians AB still has a page listing it as a product at http://webb.resilans.se/products/advanced.html but it's marked as "currently not for sale".