During the last few years, Open-source GIS software has been taking precedence over proprietary GIS software. It’s even becoming viable for implementation of large-scale, national GIS projects with a large number of users; projects traditionally supported by proprietary software. The Kosovo Spatial Data Infrastructure (SDI) is one example of this new trend. It consists of several service-oriented modules: GeoPortal, Cadaster and Land Information System (CLIS) and the Address Register (AR). All of these are designed and implemented on the FOSS stack and interconnected via OGC services based on Service-Oriented Architecture concepts. At the heart of the whole system lies the GeoPortal - the main official channel for spatial data dissemination. It provides discovery and view services for the underlying spatial data and enables ordering and downloading of the data by exposing it via its services. The main part of the AR and CLIS applications is a web-based feature Viewer/Editor which supports a rich set of feature editing capabilities including: quadratic Bézier curve digitization, digitization of adjacent polygons, client-side polygon splitting, topology preserving feature modification tool, multipolygon digitization, digitization of perpendicular and parallel lines, etc. The Viewer/Editor application is optimized to handle a large number of features without overburdening the client’s browser while maintaining a high performance level. The project utilizes many of the FOSS4G frameworks and projects such as OpenLayers, GeoExt, GeoServer, GeoWebCache, GDAL/OGR, JTS and its ports, GeoAPI, proj4, MapFish Printing service and GeoSolutions Style-editor, so you could call it a real showcase of available FOSS4G potential. Besides the standard GIS functionalities, the system offers capabilities such as importing of spatial data and feature class creation from the web interface using the GeoServer REST API, dynamic handling of user-defined styles for layers and multilanguage support for alphanumeric as well as the spatial data. Initially, there were some doubts about implementing such a large-scale solution on FOSS, but at the end of the project it has become clear that it lives up to our expectations. The presentation focuses on our experiences and challenges related to building the SDI on FOSS stack.