It also makes its appearance in a few Napoleonic jurisdictions that have partially received German legal theory, like Italy or Portugal.
A transactional act is any voluntary manifestation of intention that creates the legal effects that the actor(s) specifically intended to bring about.
The most obvious examples are quasi-contracts such as unjust enrichment, negotiorum gestio, and indebiti solutio, as well as acknowledgments, depositions, and the carrying out of a fiduciary duty.
A de facto act is involuntary and lacks any overt intentionality; instead it comes about by accident (i.e. force majeure) or is construed from the circumstances (even when they contradict an actor's express will).
Some examples of the latter include a constructive trust, partnership by estoppel, and agency under apparent authority.