Searching open source Terrain and Satellite maps for Leaflet

Question

For our project, we are exploring Terrain and Satellite maps using Leaflet.js

While exploring the Internet got this OpenTopoMap. However, not sure whether this is a Terrain Map.

For Satellite got this Esri.WorldImagery. However, as the map source is https://server.arcgisonline.com don't know whether these are open source maps or paid maps.

Also, is there any open source basemap like OSM for Terrain and Satellite maps?

Answer 1

According to this article Esri World Imagery can be used free of cost when all of the following conditions are met:

1. You have signed up for a free ArcGIS Developer account
2. You are not generating revenue from your app (in the form of advertisements or subscriptions)
3. Your users request < 1 million tiles/month
4. You properly attribute both Esri and all of our data providers