Files with fbn extension are used by Arcview program. These *.fbn extension files store spatial index for read only datasets.
Software that open fbn file
FBN file extension - ArcView spatial index file
What is fbn file? How to open fbn files?
File type specification:
The fbn file extension is associated with Arcview application, a desktop GIS for mapping, Data Integration and Analysis. An *.fbn file contains spatial index for read only datasets.
mime: application/octet-stream
The default software associated to open fbn file:
ArcGIS for Desktop Basic (ArcView) 
Company or developer:
Esri
ArcGIS for Desktop Basic (formerly known as ArcView) is GIS (geographic information system) application used to visualizing, managing, creating, and analyzing geographic data.
ArcGIS for Desktop Basic is a part of the ArcGIS Desktop. ArcGIS for Desktop Basic supports creation of interactive maps, spatial analysis, GIS deployment, map viewing and navigation, map printing etc.
List of recommended software applications associated to the .fbn file extension
Recommended software programs are sorted by OS platform (Windows, macOS, Linux, iOS, Android etc.)
and possible program actions that can be done with the file: like open fbn file, edit fbn file, convert fbn file, view fbn file, play fbn file etc. (if exist software for corresponding action in File-Extensions.org's database).
Unspecified and all other actions for computer programs working with fbn file - ArcView spatial index file
Click on the software link for more information about ArcGIS for Desktop Basic (ArcView). ArcGIS for Desktop Basic (ArcView) uses fbn file type for its internal purposes and/or also by different way than common edit or open file actions (eg. to install/execute/support an application itself, to store application or user data, configure program etc.).
