Don't agree that 10g EM and 10g grid are the same. I am surprized that someone asks and someone else says they are same, and many seniors are quiet about it as well.
10g EM comes with every database install... doesn't mean its a grid; it can only be used to handle that particular database. If you need to manage a host of servers under one EM, the default 10g EM will not help anyway, you will need the grid EM to be installed which is a seperate installable...
You've got to get this "Grid" thing out of your head.
It's a marketing ploy .. smoke and mirrors .. A Larry thing; remember "Unbreakable"? It's morphed into "unbreakable linux". Look for Grid-ish next year... he he
It's OK to market a product, but professionals have to realize it's just a software upgrade.
Dbconsole is a scaled down (single instance) version of Enterprise Manager. A Dbconsole license is included with your database. If you've got to manage more than a few databases, you may want to consider Enterprise Manager.
Enterprise Manager will manage multiple databases from one console. It can be downloaded and used just like any other Oracle product but you still have to license it if you use it past the 30 day eval period.