Ah, looking further, it meets all of your technology requirements. It does have multiple privilege levels, but they're not particularly fine-grained. There's a
project in the works to fix this.
The API looks pretty simple -- I hacked together a quicklinks module in about half an hour.
It's a little biased towards creating a community site, rather than a corporate site, but with the default configuration, it might be a strong base for what you're trying to do.
The notion of "taxonomy" looks quite powerful, but I've not got my head round it fully yet.
The photo album software is a bit poor. There was a hacked-on module for
gallery, but the drupal people have decided to replace it. They're not feature-for-feature yet, unfortunately.
Oh, and it's a doddle to install.