Science Magazine periodic table: a series of pictures that demonstrate how the periodic table evolved with time.

iWantToStudyEngineering: a great set of questions for high school physics or maths enthusiasts which can be really fun. For all these questions, the point is to not use complicated equations but to think outside the box and use the minimal amount of effort to solve them.

arXiv v.s. snarXiv by David Simmons-Duffin: Test your ability to distinguish real high energy paper titles from fake ones. (I thank Stephen Ebert for showing me this.)

Hyper Collocation: Find out how frequently a certain word or phrase is used on arXiv. Useful when not sure which expression to use!

IArxiv: A convenient tool for browsing arXiv papers. It provides a personalised ranking of papers based on click history.