An iwg file extension is related to ArcGIS for Desktop Basic and used for its index files.
Software that open iwg file
IWG file extension - ArcView DWG index
What is iwg file? How to open iwg files?
File type specification:
The iwg file extension is associated with the ArcView (also known as ArcGIS for Desktop Basic) a GIS (geographic information system) software for Microsoft Windows.
The iwg file stores DWG index that is created after you open *.dwg file in ArcView.
The default software associated to open iwg 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 software applications associated to the .iwg 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 iwg file, edit iwg file, convert iwg file, view iwg file, play iwg file etc. (if exist software for corresponding action in File-Extensions.org's database).
Hint:
Click on the tab below to simply browse between the application actions, to quickly get a list of recommended software, which is able to perform the specified software action, such as opening, editing or converting iwg files.
Programs that can create iwg file - ArcView DWG index
Programs supporting the exension iwg on the main platforms Windows, Mac, Linux or mobile. Click on the link to get more information about ArcGIS for Desktop Basic (ArcView) for create iwg file action.
