Rabbi Nassi’s Plurality in the Godhead, or How can three be one? is a work by a Jewish rabbi on the Trinity, on the plurality of God within the Godhead.
Basic Christian Doctrine is an anonymous Doctrines book by a Calvinistic author. It has 50 topics/chapters, and does a good treatment on these topics even if it is a briefer treatment. Each chapter has 10 points with a paragraph or two of comments on each point. Lots of verses.
The Triune God is a paper by J. Gresham Machen (1 very long chapter) on why God is triune, which is a defense of the Trinity. Being Presbyterian, he uses the Shorter Catechism.
This Christian Theology by Adam Clark is a Systematic Theology work of 37 chapters/topics including Scriptures, God, Attributes of God, Prayer, Faith Repentance, Trinity, Regeneration, the Holy Spirit, etc.
Theology for the People is a systematic Theology from 1875. Plumer deals with the Word of God, Names and Titles of God, Attributes of God, the Trintiy, Creation, Providence, etc.