off-the-shelf

既成の、市販品といった意味のようですね。

(idiomatic) As purchased or as commonly available, without modification or customization.
We can build a specialized part for you, but an off-the-shelf product will probably cost less.

"Programing Python" CHAPTER 1 “Programming Python: The Short Story”
The Taskに以下のような一節がありました。

Naturally, there are off-the-shelf programs for managing databases like these. By writ- ing a program for this task yourself, however, you’ll have complete control over its operation.

市販品はあるけど自分でプログラムを書けばその操作を完全にコントロールできると。

Programming Python