Sri Lanka: time and a half, capped at twelve overtime hours a week
The Shop and Office Employees Act sets eight hours a day and 45 a week, and requires overtime at not less than one and a half times the ordinary rate. The unusual part is the ceiling: no more than twelve overtime hours may be worked in a week. That is a limit on the hours themselves, not on the rate, so beyond it the question stops being what an hour is worth and becomes whether it may lawfully be worked at all. The calculator caps the effect accordingly.
The 45-hour week is normally spread over five and a half days rather than five, with a Saturday morning on the end, which puts the ordinary day a little over eight hours and makes the half day the awkward unit that statutory leave has to be deducted in. That is why the days-per-week field opens on 5.5 here and on 5 nearly everywhere else, and it is worth correcting if your employer runs a five-day week instead.
Annual holiday is fourteen days, but only after a full year of continuous service; the entitlement in your first calendar year is pro-rated against the quarter you joined in, so a first-year employee is spreading the same salary over more worked hours than a colleague of two years' standing.
None of this covers everyone. Factory and estate workers fall under the Wages Boards Ordinance rather than the Shop and Office Employees Act, and their hours, overtime and holidays are set trade by trade by the relevant wages board.