(i will eventually add commentary to each page)

You can navigate all the boards on this site with your arrow keys left and right arrow keys. And if a position has multiple variations, there should be indications on the board that you can click.
Sources for the themes are listed on this page.

1. Na3

1. Nc3

1. Nf3

1. Nh3

1. d4

1. e3

1. e4

1. d3

1. a3

1. a4

1. b3

1. b4

1. c3

1. c4

1. f3

1. f4

1. g3

1. g4

1. h3

1. h4

Theoretical Endgames