AstralLein
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The interface, as I understand it, is their very first one. This is a deep demo. The mini-map isn't even made; it's just a placeholder.
The visual style was chosen for two reasons: it's very durable (doesn't become outdated) and will run on any computer. They considered these criteria more important than having impressive graphics. They also noted that several more beautiful styles in a row turned into a mess on the map. This is a side effect of modern graphics in 2D. So, they chose carefully and thoughtfully after a long consideration.