This is the fourth installment of the Fortnightly Topic Challenges Rerun described here and the forty-fifth installment of the FTCs overall, with topics suggested and voted on here. This fortnight's topic is "Flags" (suggested by Stiv) and will span from the 13th of December to the 26th of December. During this period, we will compile the list of relevant questions and post it as an answer to this question.
In the meantime, please go and propose and vote on future challenges!
Everyone have fun, and happy puzzling!
Link to other Fortnightly Topic Challenges.
The suggestion is copied to this post for posterity.