We propose a Logical Framework for labelled Natural Deduction systems. Its meta-language is based on a generalization of the rule schemas proposed by Prawitz, and the use of labels allows the definition of intentional logics, such as Modal Logic and Description Logic, as well as some quantifiers, such as Keisler s for non-denumerable-many individuals property P, or for almost all individuals P holds, or generally P holds, not to mention standard first-order logic quantifiers, all in a uniform way. We also show an implementation of this framework as a freely-available web-based proof assistant. We then compare the definition of logical systems in our implementation and in other proof assistants — Agda, Isabelle, Lean, Metamath. As a sub-product of this comparison experiment, we contribute a formal proof (in Lean) of De Zolt s postulate for three dimensions, using the Zp system proposed by Giovaninni et al.