This is the open source project Placemark, which was previously a SaaS app. Placemark is a tool for creating, editing, and visualizing map data, in a variety of formats including GeoJSON, KML, Shapefiles, CSV, and many more.

This is a monorepo and it contains multiple subprojects:

• Play is the free-to-use interface accessible at play.placemark.io. It has no server backend or map storage, but it supports all other features.
• Placemark-app is a simplified version of the Placemark SaaS app that supports server storage and realtime sync and collaboration.
• The SaaS branch contains the unsimplified, full-fledged code for the Placemark product, which is a superset of Placemark-app and includes things like billing and account provisioning.

• You need to edit, preview, create map data and want something similar to geojson.io, a project originally by the same author.
• You want to build a SaaS on this code. It is very liberally licensed. If you want to create a startup on this, you can.
• You want to extract patterns or modules from the codebase. It has implementations of many things in it.

• An alternative to Mapbox GL, Maplibre, Deck.gl, etc: it uses Mapbox GL. It is a tool for editing maps, it uses existing tech to render the maps.
• A library you can use in your app. But you could possibly extract such a library from the codebase with a bit of time and effort.
• A product with customer support. It used to be, but is now an open source product mostly developed and maintained by Tom MacWright in his (my) free time.