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While one can achieve a basic form of some of the data organisation of OO with the Mathematica Entity system, that has many limitations, it still requires far too much custom massaging.
Mathematica needs decent vendor-supported built-in Wolfram-language OO and integration of said OO with Wolfram Workbench and other IDEs
Although a valiant attempt, the user contributed MTools is home-baked, half-baked, and (because it was started some time ago), does not leverage the latest capabilities of MMA. Perhaps it is a candidate for rollover to fully vendor-supported OO.
And then there are some old "toy implementations" on stackexchange, not exactly the level of support one could recommend as an industrial strength solution to a client.