In this YouTube video, Lior Yaffe explains some design concepts that have made it into Nxt and the upcoming Ardor platform.
A detailed technical comparison of the major differences in features and functionality between the Ardor and Nxt blockchain platforms.
An overview of the advanced concepts behind the design and architecture of the Ardor blockchain platform, and the motivations for its creation as a next iteration in the development of the Nxt software.
The Nxt http API is well documented in the Nxt Wiki and can be easily tested within the Nxt client.
A Probabilistic Analysis of the Nxt Forging Algorithm - an academic paper published in the Ledger journal.