Open source GIS stack
Open source GIS stack offers a good set of GIS tools also. Here is some listed and summarised for you all - dare you to try them!
GDAL is a translator library for raster and vector geospatial data formats that is released under an X/MIT style Open Source License by the Open Source Geospatial Foundation. In scope of the challenges, the GML driven by application schemas driver can resolve the complex schemas of GML formatted INSPIRE datasets and may help with converting data into some better manageable format.
QGIS is a desktop software for creating, analysing and visualising GIS datasets. You can freely download QGIS and utilise it instantly on your computer - it works with Windows, Mac, Linux… you name it. QGIS supports GDAL/OGR data formats and has the ability to connect different toolsets like SAGA GIS and GRASS. It also has various geospatial tools and over 300 different plugins designed for special analysis.
PostGIS is an open source database software extension to PostgreSQL software. It is handy to use with large geospatial datasets and provides tools for data management and analysis.
Oskari is an open source platform for displaying and analyzing geospatial data. Oskari is a framework for easily building multipurpose web mapping applications utilizing distributed Spatial Data Infrastructures like INSPIRE. It offers embedded maps which you can tailor to your needs with Oskari API. It combines statistics with interactive maps providing the possibility to create thematic maps. You can use Oskari tools easily through different Oskari based portals like Arctic SDI, Paikkatietoikkuna or test it with dev.oskari.org.
GeoServer and MapServer
If you are interested in creating INSPIRE compatible WMS or WFS interfaces, GeoServer or MapServer are your tools. Both have the ability to provide geospatial interfaces and support for INSPIRE. Where MapServer might be a bit faster, GeoServer has a user friendly UI. You can download the services and test them locally but if you want full advantage of these software you need a server to host these software.
MapBox, Carto, OpenLayers, Leaflet
OpenStreetMap is a massive database of geographic data, and it’s all open and free. Information on how to access and participate in building OpenStreetMap data can be found at https://learnosm.org/en/