This SF story-generator spreadsheet was written by Jocelyn Paine, using Excelsior. There's an explanation of how it works at http://www.j-paine.org/excelsior/repository/spin/. Thanks to Alice Campbell for sending me an improvement.
Story	Recalculate
Earth	Recalculate
is taken over by mutant diploid armour plated pterodactyls with ESP and silicon-based DNA
and is visited by evil
aliens
who
save everyone
and depart
story node nos	story out edge count													story out edge index	story out edge destination node no	story out text
0	3													0	1	Earth
1	6													5	2	is taken over by mutant diploid armour plated pterodactyls with ESP and silicon-based DNA
2	4													2	4	and is visited by evil
4	3													0	5	aliens
5	2													0	6	who
6	4													1	9	save everyone
9	2													0	-1	and depart
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
-1	0													-1	-1	-1
node nos	out edges													out edge count
0	Earth	1	Mars	1	Planet 9 of Alpha-Centauri	1								3
1	is used as the cue ball in a game of galactic bar-billiards	2	falls toward the Sun	2	falls toward a black hole	2	is struck by a comet	2	is invaded by nasty aliens	2	is taken over by mutant diploid armour plated pterodactyls with ESP and silicon-based DNA	2	is taken over by a time-travelling loony who returns to his youth and	6
2	and everyone dies	-1	and almost everyone dies	-1	and is visited by evil	4	and is visited by good	4						4
3	changes sex, meets himself, and has children who become	7	kills himself (I said he was a loony)	-1										2
4	aliens	5	robots	5	mutant brewers yeast cells	5								3
5	who	6	who	17										2
6	also die	-1	save everyone	9	rewind time to before the disaster	11	copy the lot into a giant Sextium 3000 and edit out the nasty bits	16						4
7	yet more of this loony who	3	the whole human race	-1										2
8														0
9	and depart	-1	and give the secret of	10										2
10	free fusion power	13	free beer	13	Life, the Universe, and Everything	42	Life, the Universe, and Everything	13	eternal life	13				5
11	but then	0		9										2
12														0
13	so everyone gets very bored and tries to forget this by	15	so everyone gets very bored and tries to forget this by	14	so all live happily ever after	-1								3
14	drinking	-1												1
15	becoming Gods; creating a new Universe wherein	0												1
16	but the system crashes	-1	but they mis-type 'aliens' and take out all the lions instead	-1	but they run out of credits	-1	but they run out of budget	-1	but they run out of CPU time	-1	but they run out of memory	-1	but the editor is in Prolog and they know only Basic	6
17	are wiped out by	18	wish only to serve everyone	21	save it and enslave everyone	-1	and	22	are converted by the village priest (who tells them of God) to	26	steal its reserves of	27		6
18	mumps	19	atom-test radiation	19	the village idiot	19	the beer	19						4
19	which then kills off everyone else	-1	which then turns everyone else into supermen	20										2
20		-1		13										2
21	(fried)	-1	(boiled in white sauce)	-1		-1								3
22	are stopped by a logician	23												1
23	who says 'I am lying'	24	who can't remember the Paradox of the Liar and gets killed	-1										2
24	and so he must be telling a falsehood	25												1
25	so he must be telling the truth	24												1
26	good ones	5												1
27	water	28	iron	28	asparagus soup	28	beer	28						4
28		-1	and	22										2
29														0
30														0
31														0
32														0
33														0
34														0
35														0
36														0
37														0
38														0
39														0
40														0
41														0
42	42	13												1