loads of reusable solutions based on your requirements :).
CMS? CRM? ERP? normal / headless? API-First? Content-First? Mobile-First?
It's about approach and planning, what does the customer need? what does she/he wants? How much money are they able to spend.
Is it better to just direct them to a highly specialized team of CMS engineers who provide a cheap adequate solution with little flexibility within a certain price range? Or is a custom engine better ?
Personally I rarely reuse code that is not a core engine update I wrote to make my life easier accessing and controlling data flow.
For example using Annotations to define the Property-Exports and combining them with the appropriate ACLs.
Others will put this in the data-warehouse. Others maybe are more likely to reuse their libraries because they are so specialized.
I jump technologies way to often, so usually I come back face-palming about the crap I wrote the last time :)