I would be nice to have a web page that a DM could monitor / manipulate all of the Player Characters in his campaign all on the same page.

For each Player Character you would display these items of information

Primary items: Name, Picture, Level, Hit Points 

Optional Items: AC, Weapons Hit/Damage

I think a DM screen needs name, race, class, level, HP, AC, saves, and spell slots (in real time without having to refresh).

Optionally, a quick link or tab to view skills, spells, and equipment.

If they ever incorperate a loot/shop inventory for DMs or a vehicle inventory for whole party, this should be here also.