Very close to, but not quite.
Up to a null set; except for a set of measure 0.
Up to, except for a negligible set (where negligible is not universally but contextually defined).
Something or someone that doesn't quite make it.
Almost but not quite.
Of a covering space of finite index.
In essence, but not in fact.
By computer or in cyberspace
Of a substructure of finite index.
Without exaggeration.