More flexible APIs: https://github.com/graphql-java/graphql-java

Automatic dependency review: https://www.sonatype.com/software-bill-of-materials

Akka and monitoring: https://sematext.com/blog/2016/10/31/akka-monitoring-with-kamon-and-spm/

Code forensics: https://github.com/adamtornhill/code-maat

How to design large-scale systems: https://github.com/donnemartin/system-design-primer/blob/master/README.md

Developer roadmap: https://github.com/kamranahmedse/developer-roadmap

Test impact analysis, to identify which tests to run: https://martinfowler.com/articles/rise-test-impact-analysis.html

Graph database, for knowledge systems: https://grakn.ai/

Plain old graph database: https://neo4j.com/

Lockless concurrency: https://assets.bitbashing.io/papers/lockless.pdf

Deep learning, for Java: https://deeplearning4j.org/