This work presents a collection of examples illustrating typical uses of what is referred to as a Brief Theory of Almost Everything. The central idea is that many systems from different domains can be described in terms of: - a space of states, - admissible transformations, - and a constraint functional C, which measures deviation from admissible conditions. The document does not introduce new models, but rather shows how existing mathematical and physical structures can be interpreted through this perspective. In many cases, the constraint functional C is not chosen arbitrarily, but can be derived directly from the underlying structure of the problem. Examples include linear systems, vector calculus, quantum systems, and discrete constraints. This is a preliminary version intended for feedback. The presented constructions are illustrative and do not claim optimality or completeness. All ideas in this document are original to the author unless explicitly stated otherwise.