Declarative Debugging https://www.metalevel.at/prolog/debugging (Prolog is amazingly flexible in what you can comment out and still have a runnable program)
miniblog.
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The Shelf is a NeXTSTEP alternative to a clipboard, but more flexible and powerful: https://en.wikipedia.org/wiki/Shelf_(computing)
You can put a source file and destination directory on the shelf, enabling a cut-and-paste style operation. You can still refer back to them afterwards!
"The framework provides the following, or you can plug in anything you like." Focus on what you make easy! An empty program is flexible too.
Apple Dylan Screenshots
https://web.archive.org/web/20140703072127/https://opendylan.org/about/apple-dylan/screenshots/index.html
An IDE where all your code is modelled as objects with metadata is amazingly flexible.