Keep a Changelog!
I'm a big - big - fan of changlogs and how they can help your team. I gave a 5-minute lightning talk about them at my work late last year and wanted to share my slides with you. If you are interested in changelogs, take a look at some of my repositories on my GitHub Profile
Offheap Bloom Filters
Bloom filters are a really cool data structure that trade a small amount of bounded memory use to protect slow resources like databases or network requests. Because they deal with direct bytes, they are also great candidates for off-heap storage within the JVM.