All MMOs should have either a built in system, or an add-on if such exist, like Altoholic from World of Warcraft.
This incredibly useful little addition to the game gives you instant access from any character to information about all the other characters you have in game. So their class and level, the money they have at present etc. But it goes much further than that:
The real power of this add-on is the ability to see all of your other characters’ current equipment in detail. So if you’re a crafter like I am, you can see at a glance whether the items you can make are good upgrades for other characters – without endless logging back and forth between alts!
The system goes even further; it allows you to look at the crafting professions of all of your characters to see the list of recipes known so you can see who can make what and what materials they might need to do so.
It’s a wonderful addition to the game, and I miss it in every other MMO that I play…