Louis Berkhof's Systematic Theology, unabridged, online, free.
Justin Taylor explains, at the link, and below:
Berkhof (1873-1957) was born in the Netherlands, and his family moved to Grand Rapids when he was 9.
After graduating from Calvin Theological Seminary and Princeton Theological Seminary, he returned to Calvin and joined the faculty. For the first two decades he taught biblical studies, and then for almost two decades after that he taught systematic theology. He also became president of the seminary in 1931 and continued so until his retirement in 1944.
His Systematic Theology was published in 1932 and revised in 1938.
Wayne Grudem has said Berkhof’s Systematic Theology is “a great treasure-house of information and analysis . . . probably the most useful . . . systematic theology available from any theological perspective.” Richard Muller calls it “the best modern English-language introduction to doctrinal theology of the Reformed tradition.”
It tends a bit toward proof-texting‚ which is not to say that Scripture is regularly misused but that he does not generally show his exegetical work. Further, the book is not very original or creative. In many ways, it is an English summary of Bavinck and a compendium of mainstream Reformed theology.
But having read every word of this influential work, I have no hesitation in warmly commending it as one of the most useful ways to get an excellent summary of virtually all areas of systematic theology.