Link to other Fortnightly Topics.

This is the seventh installment of the Fortnightly Topic Challenge described here with topics suggested and voted for here. This fortnight's topic is (suggested by rand al'thor), and will span from Apr. 9 - Apr. 22. During this period, we will compile the list of questions featuring this topic and post it as an answer to this question.

In the meantime, please go propose and vote on future challenges!

Everyone have fun, and happy puzzling!!