Playing THIS with THAT. . .

[The_Gneech]

In 1982, I ran a Star Wars game using AD&D (Oh, the irony!) with a single player. Kinda-sorta worked, but not really.

In 1985, I ran a Star Wars game using Traveller. Worked better, but not that much. Ship combat was a drag.

From 1987 - 1990, I ran a Star Wars game using various forms of the HERO System, starting with Robot Warriors and going on to Star Hero (First Edition). Worked beautifully for character-to-character stuff, sucked for ship combat. During this period, WEG came out with the original Star Wars Roleplaying Game which I cheerfully plundered for source material, but almost never actually ran or played.

I'm noticing a pattern here.

From 1987 - 2000 I generally used the HERO System for everything and both ran and played a wide variety of games from pirates to pulp heroes to Musketeers to superheroes, but as it's a "meta-system" and designed to simulate genres, it doesn't really have that "crazy mix'n'match" thing that the OP is talking about going on.

-The Gneech

 

[Fenes]

I have had crossovers between Shadowrun and D&D (both 2E and 3E). I usually did those by running it character centric - meaning, if a D&D PC did something, D&D rules were used, if a SR PC did something, SR rules were used, and rule-of-thumbed the conversions on the fly (SR Stats = D&D Stats/3, etc.)

 

[Herobizkit]

Back when AD&D had a "2" in the edition, I DM'd a Robotech campaign using a hybrid of Palladium and the AD&D2 rule set. It was probably one of the most entertaining campaigns I ever ran; I pretty much invented rules on the fly when the two systems didn't mesh so well, and the story I had on the go was worthy of most action/comedy serials on TV.

 

[Flynn]

I've been enjoying using Savage Worlds to play a D&D-style fantasy campaign. The flavor is very "old school", and the players are enjoying themselves immensely. I've even been documenting my progress here:
http://www.enworld.org/showthread.php?t=213056

I've also done the same with HERO System, but after a series of bad experiences with a HERO-style Rules Lawyer, I won't be going back to that system again any time soon. The system worked well; that was just a personal issue that was non-game-related.

Enjoy,
Flynn

 

[Mallus]

A strong argument could by made that my current, almost four year old D&D/AE mashup campaign qualifies as a 'THIS with THAT' game. The general consensus is that it bears a slight passing resemblance to D&D. There's a Story Hour. We even update it. Occasionally.

 

[Aus_Snow]

Interlock for fantasy, check.

 

[LostSoul]

I've been playing D&D using Prime Time Adventures (D&D soap opera was the concept; series name is The Days of our Lives on the Keep on the Borderlands). It's been very cool. I try to use explicit D&Disms when I can - like casting Animate Rope on a bridge that was about to crash to the ground, killing the Prince-Regent I had sworn to protect.

My PC's Issue is Guilt: He had sworn to protect the King (like his father and his father's father before him), but the King left for the Dungeons of Dagorath without me, and since disappeared. He also feels betrayed by this, which he takes out on the Prince-Regent.

It feels very much like a D&D story - except that we don't have to worry about TPKs or power imbalances or anything that might get in the way of the story.

 

[Pbartender]

I'm pretty convinced that system does matter or, more succinctly, your Dread Ravenloft games aren't going to be anything like your AD&D Ravenloft game. . . so you ever play THIS with THAT games?

Actually, I ran just that one last fall... It was a Dr. Who based campaign set in Victorian Age Europe, using Dread as the ruleset and Return to Castle Ravenloft as the basis for the adventure plot. It worked reasonably well, but my players weren't really into that particular sort of genre (horror) or ruleset (rules-light storytelling).

Other Settings (Adventures) using Alternate Systems I've run in recent memory...

Gamma World (Famine in Far-Go) using True20.
Rifts (Sunless Citadel) using D20 Modern.
Star Wars (Lords of the Expanse) using Spycraft 2.0.
D&D (Isle of Dread, White Plume Mountain, Tomb of Horrors) using Iron Heroes.

 

[Rechan]

I think Eberron with Spirit of the Century would be fun.

Eberron with the DFRPG, however, would Rock my Socks.

 

[buzz]

I think Eberron with Spirit of the Century would be fun.

It is! http://forum.rpg.net/showthread.php?t=318449