Frab – free and open conference management system
From Frab's schema.rb:  create_table "people", force: :cascade do |t|
    # ...
    t.string "first_name", limit: 255, default: ""
    t.string "last_name", limit: 255, default: ""
    t.string "gender", limit: 255
    # ...
  end

Our schema has a similar table, but with "prefix" instead of "gender", where on the front end a list pops down with Mr., Ms., etc. We just use the prefix to form the full  name.I wonder where the need to track gender comes from in such an app. We manage events and conferences too, but gender hasn't come up beyond the salutation. Since they do care about gender maybe they will soon also want pronoun and possessive_pronoun columns.