We ♡ open-source. In 2017, we started OpenMapTiles - the first truly open project for generating vector tiles, and we still keep maintaining this project. The community around is very active, with dozens of commits each month.
Last year, we were one of the financial sponsors of support for vector tiles in QGIS. Also, we developed an open-source plugin for easy loading vector maps in QGIS.
We were also one of the founding members of the MapLibre community and significant contributors, mainly with the MapLibre Mobile SDK.
If you want to learn more about our open-source activities, attend one of our talks at FOSS4G 2021! There is a free tier for testing, personal use, and open-source communities, we also have an on-premise solution for offline serving of tiles from MBTiles, GeoPackage, and PostGIS.
For more info, have a look at maptiler.com :-)