Double dip / special mechanics

[Shadowmod]

I looked up the double dip mechanic in the wiki, and unfortunately its article is but a one-liner which does not really explain much of any of the details. A forum search for games using that mechanic also has not really turn up much of anything (one game by petroleumjelly, which seems to have been abandoned on D2...
So is the double dip mechanic used to determine one lynch with two votes or to allow town to actually lynch two players each day?
And if it is the latter, how is this kind of mechanic usually implemented?
(1) Once one player has reached the lynch threshold, the player with the second highest amount of votes is lynched with him.
(2) Day only ends when two players have reached lynch majority.
(3) Like (2), but once the first player has reached lynch majority all votes on that waggon are locked in place and the players have to pick a second target among the remaining players.
(4) Something else I did not think of?

Has any one played in or modded a game which used a double dip mechanic?
Is there a list of games that did?
And how did it work out?
If you had to chose between the mechanics listed above, which one would you prefer?

On a somewhat related note, I would be interested to learn whether there was ever a game which used any mechanic that would bring players into the game later (i.e. players would not start out playing right from D1 but would only be brought into the game at some later point)?
If there are such games, I would appreciate a quick link to that game and maybe a short report about the experience if you were in that game, whether the mechanic worked well and was interesting or just caused players who were not in the game yet to lose interest quickly?

[callforjudgement]

In terms of people joining the game later, there has been at least one Angel Nightless game like that (War in Heaven III), but it didn't end well. The basic idea was similar to replacements, but arriving at set times and without any obvious connection between the players who replaced out and the players who replaced in, and nothing forced the numbers to match exactly. In the case of War in Heaven III, IIRC almost all the scum flaked pretty early, which might or might not have had anything to do with the mechanics. Here is the mod's comments about the mechanic in question. The players weren't massively enthusiastic about the version of the mechanic used there. (I wasn't in the game, but I was watching. It was eventually abandoned as a result of a server crash followed by insufficient enthusiasm to restart it, so it's hard to say how things would have worked out.)

I was also in a Worst Roles Mafia game where one of the players could recruit players from outside the game in (basically getting the mod to send them a role PM to see they started playing). That was pretty meh in terms of how it worked out; it worked for that game but it's not a mechanic I could imagine expanding to other games and working well.