This is Firefly, a theme for Tumblr.
A wonderfully refined, super-customizable powerhouse. The base was originally designed to be used as my very own development log, yet I decided to expand and share the theme.
Customize Firefly to create a blog that’s perfect for you and your unique needs. Choose between a single-column and multi-column layout, customize the typographic palette, display your latest tweet and much more. Firefly is available here.