From home page:

The MONDIAL database has been compiled from geographical Web data sources listed below:

• CIA World Factbook,
• a predecessor of Global Statistics which has been collected by Johan van der Heijden.
• additional textual sources for coordinates,
• the International Atlas by Kümmerly & Frey, Rand McNally, and Westermann,
• and some geographical data of the Karlsruhe TERRA database.

Openness: OPEN (?)

• Most data is PD (but not all ...). Clearly intended for reuse but no explicit license given.