Check out AccessibleModels.jl: Automatic UI and Model Fitting for Arbitrary Objects : it builds on the positive experience creating and using this package, improving further.
AccessibleModels.jl provides a uniform model definition syntax for a bunch of backends instead of Optimizationjl-only here. Backends include optimization, MCMC sampling, and even UI generation.
I consider AccessibleOptimization.jl effectively deprecated now: it still works fine, but AccessibleModels.jl has all its features & more, and I recommend using that package instead.