Someone on Mastodon asked about running adventures in systems other
than the ones for which they were written, and since I do a lot of
that, it gave me to think…
I'm currently playing in The Pirates of Drinax converted to
GURPS, I've recently run the Alien RPG adventure Chariot of the
Gods in FUDGE, and I run all sorts of things in Cthulhu Eternal
even though they're not written for it. Why?
I start off from the idea of the game rules not being a physical
reality, i.e. there is a real world of the game that the rules (in
order to be playable) can only roughly represent. Sure, there may be
magic and ultra-tech and whatever, but people still work like people,
they don't get superhumanly tough without superhuman powers, they're
still in trouble if they get shot or fall too far, and so on. (I know
D&D and Pathfinder players who regard the fiddly mechanical
details as a direct representation of the game world's reality,
including classes and levels and stuff, and that really doesn't work
for me.)
So I don't feel bound to use a particular rule set in the first place.
And then I want rules that I feel comfortable with, that can do the
job of providing answers to questions of world-reality (like "how long
does it take him to pick the lock?") without breaking when I just make
a casual ruling without invoking the full weight of mechanics.
GURPS fits that niche very well for me, in part because I've been
playing it on and off since the 1990s and consistently since the
release of 4e in 2004 (and occasionally writing for it too). It's a
language I speak fluently; given a situation, I can readily work out
how to model it and who should roll against what. There are large
parts of it I don't use, or only use when it seems interesting; a
replacement for it is permanently on the back burner, but it's going
to be a lot of work.
A secondary benefit to GURPS in particular that also applies to the
other systems I favour: most of the time a player can describe what
they do not in rules terms but in terms of what the notional person in
the notional world would do (e.g. "I want to hit him, but carefully;
I'm more interested in not letting him hit me") and I can turn that
into the rules that are needed ("OK, that's a Defensive Attack: same
chance to hit, reduced damage, better defences"). And the player who
does that is not at a disadvantage relative to the player who has
learned all the rules. I'm generally happiest playing this way rather
than in pure rules-speak.
I use Cthulhu Eternal for most Lovecraftian gaming because it's a
percentile system familiar to Call of Cthulhu players, but it's not
encumbered with the rules bloat of CoC 7e, and if I want to publish
things for it I can, without faffing around with licencing deals that
can be changed at a whim.
FUDGE is similarly free, and gets the job done without needing lots of
work.
This isn't the "don't want to learn new rules for a new campaign" that
I think pushed the development of universal systems in the 1980s; very
few modern games are as complex as those could be, so the burden of
learning a new system is much less. But it is more "here is a system
with which I am, and my regular players are, comfortable, that can
help me achieve the atmosphere and goals that I want".