Flabbergast: a programming language for generating configurations

This looks nice and the syntax is very similar to HOCON. One thing I like about HOCON in general is that everything is "overrideable"/"mergeable". This is nice because I can have a config set of defaults that needs no other config to run. From skimming the manual here I see that I have explicitly say something is a template or not. But I definitely like that I can make it clear that I require values.

Looks great. Sorry, I don't have much more feedback than that, but I will say I fear the typing and inheritance may make it more complicated than configuration end-users want to deal with.

Very interesting! The missing piece seems to be versioning on the libraries, for example:

lib:apache/aurora/0.5.x

Without this, I can imagine a new version of Aurora introducing a new required config field, the Flabbergast library being quietly upgraded to handle this, and then users seeing inconsistent behaviours.

Remember that config file formats are one of the least well-behaved pieces of a software's public API (prone to breaking changes in even MINOR releases), so it seems sensible to build this in from the start.