What does it mean when somebody dies by “unknown reason?”

It was a one-time item given out by the developers to beta testers. Using it sets your AP to 30/6. It doesn't count as a drug for the purposes of the "Clean" status (i.e. you're still clean after using it).

It's marked a "Professional tool" and therefore can't be dropped. If a person carrying one does manage to drop it somehow (i.e. by dying) it can't be picked up again by anyone else.

Maybe a late answer, but i used the adjustable spanner to open a food crate. so it can be used to open certain heavy objects.

i also used it to help 2 zombies to the next life.