@Zuenie I can only think of Geoserver providing the capability to spatially adapt the data (spatial queries do you mean?), but I dont know about report generation even in Geoserver.
But why would they want to do this spatial analysis? You can just ask them to tell you how they want to spatially adapt the data, you can do it in GIS software and generate reports for them instead of making an application for them to do that themselves. If they start learning how to do this kind of stuff, your job role as a GIS guy may soon become irrelevant.
@Salman Thank you for responding. I just want to let the user draw, edit (like pull vertices) and save data. No complex stuff. The report generator should be makeable by using maps exported as a picture. Then the webapplication should be able to create jpg's out of maps. That should be possible right? Anyhow, ArcGIS online is the most advanced, easyest to use, most expensive thing that gives me some of the functionalities I need. Are there alternatives? Other than geoserver/leaflet/html