forallx: the Mississippi State edition is an open source logic textbook. It covers propositional logic and introduces (although does not cover in as much depth) first-order logic. Email me if you’re a logic instructor and would like a PDF copy of it. A paperback copy can be purchased here. The source files, which can be downloaded and modified, are available in this GitHub repository.

The natural deduction system in the textbook can be used in Carnap. Here is a syllabus, and here is a more detailed calendar.