Every programming language should have something akin to the Ruby QuickRef or Python Quick Reference. These dense but easy navigated guides provide easily forgotten information about the most frequently used features of a language.
“How do I do a regex again? Ah, that’s right.” That’s what a quick reference provides.
I intend on starting a Scala QuickRef and hosting it (both the “source” and the user-facing site itself) on GitHub for collaboration.