I've found out that stop(nil) crashes PICO-8. Not that it's a particularly useful call, but it definitely must not crash the console.

Version: 0.2.0c
Platform: Linux 64bit
Example cart:

$ cat stop-nil-segv.p8
pico-8 cartridge // http://www.pico-8.com
version 21
__lua__

--this segfaults:
stop(nil)

$ pico8 -run stop-nil-segv.p8 
Segmentation fault (core dumped)

Fixed in v0.2.0d.