Bazel – Correct, reproducible, fast builds for everyone 11 years ago
Maven doesn't work so well when there are loads of small self contained 'micro-libraries' (yes, sub-projects, but they are so involved to set up they almost defeat the purpose). Was considering pants -- which doesnt seem like it has great adoption? -- but this seems like its substantially more fully featured.
Presumably will also make opensourcing internal projects easier. That can't be a bad thing :)