We switched DM duties for the regular D&D game a few months back. Between the summer vacation schedule conflict, lots of miscellaneous personal schedule conflict, and an apparent lack of enthusiasm for the campaign at its current place by players and DM alike, we have not been playing much.
I am not ready to take over the full time DM reigns again just now but in an effort to keep the creative juices going and the group connected I am going to run a one night, who ever shows up is good, d20 Past game. A few years ago I developed an environment I called Victorian Shadows. It is roughly based on the d20 Past Shadow Stalkers framework. The time and place is the 1870s greater London. The character level is low (currently 2nd level) using d20 modern character types with limitations of the time period. The d20 Past is not a bad source book to help you along in a campaign like this, though I don't use it completely RAW. There are some house rules for hit points which follow a wound/vitality point model, and a few other house rules as well but nothing earth shattering. The campaign is very low magic, and at this time the players have almost no access to magic while the bad guys have greater access to ritualistic magic. The good guys are part of a loose and secret alliance called the Legion of Light, and their only goal is to combat shadow which is being encouraged and used to gain power by a different secret alliance know as the New Vision Fellowship.
I have not run one of these games in a couple of years, but usually they are great fun. There have been lots of dark London foggy nights, strange happenings tied to real historic events, players acting out Victorian era characters speech styles, and heroic low level risk taking to make the whole thing just a joy.
Since I don't know who and how many will show up for an outing I have to be flexible with my adventures. I make a core adventure but adjust it around depending on the number of characters and their classes. Monsters are no problem - I have plenty of monster manuals, just pick something out of appropriate level and change the description to fit. Besides, the most dangerous monsters are the NPCs in the New Vision Fellowship.
The hardest part is fighting my urge to tie all these adventures together. I love it when plot strings tie out, and bits of information in one adventure become useful in another. To me that makes the world seem more alive. However, I must be careful that no information from a previous adventure is needed to solve a problem in the current adventure. The other challenge is completing each adventure in one evening. I have to make sure there is just enough adventure, not too much or too little, so it can be solved in one night. At the end, you just have to be tough with the party, if they have not solved the problem by the time to go home then allow the bad things to happen to the world. Hopefully they know the DM will do so, and keep the urgency in the play which makes it so exciting.
I miss running a character, but I also miss playing with my friends overall - so the DM job is not so much a chore, just my second favorite job in the game after running a character.