phpBB3 has an excellent permissions system.
One area I would like to see improved for phpBB4 would be multiple local permissions. What is a local permission for those not knowing? Well its the idea that in certain areas (forums) you have different permissions, you can post in one but not in another.
Take a bug tracker modification, with local permissions you can grant fine grained permissions based on a product rather than all products. With a download modification you allow download only from specific areas and uplaod maybe to others.
Local permissions are a very useful tool for a modification.
Currently to have multiple local permissions in phpBB3 there are a couple of options but it would be great if it would be as simple to add specific local permissions is it as for global ones currently.
If the concept of roles is kept they should also fully support multiple local permissions.
Does anyone else think this would be a useful improvement to the permissions system?


