TOPIC:

Looking for some clarity on the rules please.

Is it OK to run two instances of OpenTTD and log in to the same server twice with one set of credentials? It appears to me this is the most effective way of using dual-screens.

Cheers

It's ok if you don't create another company, join an existing company or use it for voterestart the map. So login twice with the same account in diferent pc's it's not such a good idea.

Basicly you can join spectators ...

as a complement to tomate's words:

the main and global idea is: Play fair!
and it's fair that 1 person can make 1 company, and it's enough to keep you busy building, if well played. Joining with a second instance of OpenTTD makes us question if you're playing fair because there's several exploits/unfair advantages that can be used with this behaviour. therefore, and as tomate said, not such a good idea.
and you can always use the 2nd screen to visit our forum, our rules page, OpenTTD mechanics , global OpenTTD wiki or whatever usage you want. that's my opinion

There is not many reasons to login with dual instances unless u want to watch company or see the spec chat