Since the GSDG threads aren't always going to be active, in case you need to look up or make a post in a certain one, here's a link to all the current ones for your ease of use.
Character Builds - Basic archetypes for what equipment a character can use
Classes - Ideas for character classes
Djinni - Ideas for new and rebalanced djinn
Enemies - Ideas for new enemies for use
Equipment - Ideas for equippable items
Items - Ideas for consumable and key items
Jupiter Adepts - Ideas for Jupiter Adepts
Mars Adepts - Ideas for Mars Adepts
Mercury Adepts - Ideas for Mercury Adepts
Music - Ideas for new music for the DG and where to put them
Plot Ideas - Ideas to be included in the plot
Psynergy - Ideas for new and rebalanced psynergy
Summons - Ideas for new and rebalanced summons
Venus Adepts - Ideas for Venus Adepts