Aside from the number of players (and reduced numbers in scrums, lineouts and substitutions that go with that) there are only three significant rules differences between sevens and fifteens. 1. The time allowed for penalty and conversion kicks is reduced. 2. The team which scores will restart with a drop kick rather than the team which is scored against. 3. All kicks at goal (including penalties and conversions) must be drop kicks. Tees are not allowed in sevens. Other than those three points, the rules are essentially identical. The IRB website lists the official amendments from the 15s rules which you use in 7s. See
I'm not going to go into a lot of detail but yes they do often take free kicks and drop goals, NZ and Samoa are the main treams who I always see taking this option and who can forget South Africa kicking a drop goal to win the final against England a few years back? Epic.
