Over the years I've taken copious notes on various topics of philosophy. In case anyone is interested, I'll link to several sets of such notes here. First, here are reflections on Roger Scruton's history of modern philosophy, with more extended thoughts on Wittgenstein's famous "private-language argument."

Second, I wrote notes on George Novack's Marxist history and critique of philosophical empiricism since the seventeenth century.

Third, here's a long summary of two classic commentaries on Hegel, namely Jean Hyppolite's Genesis and Structure of Hegel's Phenomenology of Spirit and Alexandre Kojève's Introduction to the Reading of Hegel. Because it's Hegel, be prepared to find it incomprehensible.

Fourth, I took notes on French philosophy in the twentieth century.

Also, you can check out some thoughts on Hellenistic civilization, particularly on its philosophy and culture.

Last, I've taken notes on left-wing sociological scholarship. Here's one set of such notes.