Python Ants. Pants started off as a python script to automate creating modular Ant builds. The `s`is important. There would have been no need if the Ant setup wasn't modular / multitudinous. The Python script setup recusive ant invocations to satisfy data dependency ordering.
The slowness of that recursion - ant / jvm have alot of startup overhead - led to the bang syntax (add ! at the end of a target address on the command line and that would trigger Pants to try to collapse the recursion from strict individual to as batched as possible - sound familiar!?). We no longer have bang syntax but we do have versions of the bang algorithm although not called that any longer.
That jvm overhead also led to nailgun., etc.
And having to support custom xml snippets employed by users of the modular ant builds led to 1/2 the reason for BUILD being plain python. That allowed those custom snippets to be easily ported by modular ant build users on their own with a few lines of Python. Expedient choice for a 1 man part time team, but legacy to drag along.