An isff file extension is related to the Intergraph Standard File Format used for hierarchical description of objects.
Software that open isff file
ISFF file extension - Intergraph Standard File Format
What is isff file? How to open isff files?
File type specification:
The isff file extension is associated with the Intergraph Standard File Format used by Intergraph Process, Power & Marine software for the design, construction, and operation of plants, ships, and offshore facilities.
The isff file contains hierarchical description of objects only.
The default software associated to open isff file:
Intergraph Process, Power & Marine 
Company or developer:
Intergraph Corporation
Intergraph Process, Power & Marine (PP&M) is modeling tool used to design, construction and operation of plants, ships and offshore facilities.
List of recommended software applications associated to the .isff 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 isff file, edit isff file, convert isff file, view isff file, play isff file etc. (if exist software for corresponding action in File-Extensions.org's database).
Unspecified and all other actions for computer programs working with isff file - Intergraph Standard File Format
Click on the software link for more information about Intergraph Process, Power & Marine. Intergraph Process, Power & Marine uses isff 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.).
