So the group I DM for (I call my "Work Group" since most of the players originally started at my place of work) - we usually do bi-weekly games.
Well a few of them have been itching to make it weekly - but I know that several of them have kids, and such and may not be able to commit to weekly games from their spouses and kids.
So I decided to DM an "Off Week" game (falls on the same day, just not the day we play our normal game; or if enough people are not present for the normal game on the normal week; if there's enough for the Off Week we just do the Off Week).
Now since the Off Week is "play if you want" - I wanted to make it easy as to why players can appear and disappear each session.
So I came up with an idea that an (evil) Wizard named Mordak (sound familiar?) has this tower on the main continent (Tawaim - easy to see how I named that continent right?) - and has this massive tower, known for possessing a ton of knowledge, so a lot of people turn to him. He always offers to help - but at cost - he marks the individual's neck with a rune and says "Whenever I need you I will summon you." And he literally summons them to his side by casting a spell and tracing that person's unique rune.
Now the players, all of whom have been slaves of Mordak have learned the summoning spell - but it takes at least two of them to make it work (this is because I always want at least two people for the off week game). So the players can spend an hour (not actual time, but game time) casting this spell to summon their companions.
I've called these games "Servants of the Wizard"...
Now the party members, obviously don't enjoy being Mordak's slaves... and they've learned on this new continent, all kinds of magic is being discovered - ancient magic. And Mordak has forbidden his slaves from going there (fearful they may yet find a way to break his summoning spell).
So the first adventure is two Warlocks, and a Rogue (the story is the rogue heard of Mordak's stash - tried to sneak in and steal something - got caught - but rather than killing the rogue, Mordak enslaved him with a rune on his neck, to use him later to steal from other wizards!) - all boarded a ship (using the Rogue's forgery skill, since Mordak forbids his slaves to travel to the Broken Lands)...
Season 1:
http://tawmis.com/kneurth/adventure-not ... -wizard-01
And Season 2:
http://tawmis.com/kneurth/adventure-not ... -wizard-02
These have been very fun, because I literally have NOTHING planned. The first adventure, I had a piece of paper that said, "boat, beach, goblin, manor" - everything that came after was all improvised. These sessions are VERY heavy reliant on roleplaying.