Not exactly what you were asking for, but I really like Soulver [1]. It's a natural-language-ish calculator. The interface is similar to a REPL where you can name/recall and evaluate. The only downside is it's a bit pricey at $30.
In version 2 you could make independent files and put them anywhere. It seems, though I may be wrong as I haven't used v3 much, that they want you to keep all your files in one central location and not have independent Soulver files.