There are other ways to extend your work with ArcGIS server without Portal, that is when you run in usage limitations, You can check, usually be open to implement multiple solutions, there is no one solution that fits all, portal. web app builder and others, now I suggest to go hybrid and expose your arcgis server to external libraries to be more open and more standard compliant you can try ESRI GeoPortal Server Esri Geoportal Server | Open Source Metadata Management GeoNode www.geonode.org + cartoview http://www.cartoview.net terriajs TerriaJS - Geospatial catalog exploration library you can combine any data source and create your catalogs via services or manually, this viewer is probably the richest in terms of geospatial content you can view in your map
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