This looks like what is left of a Raleigh Roadster (or 3rd world clone thereof), which would have had an enclosed chain case requiring a removable seat stay to service the rear wheel:



Note also the rod-actuated brakes, requiring special rims with the brake track adjacent to the spokes, notorious for poor performance and for which parts are scarce outside of the 3rd world. Depending on the manufacturer, you could also find non-standard (i.e. Whitworth) threading in various places and non-standard dimensions for bottom bracket width, wheel diameter, etc.

It could be converted, but it might be a pile of work.