You can find a showcase of the special modes and modifiers here.
Modes
Normal (The default mode. Return to this mode anytime by pressing ESC.)
Insert (Edit the world, as you normally would. Default keybinding: i.)
Replace (Replace blocks with others. Default keybinding: r.)
Modifiers (All unbound by default!)
No Clip (Fly through blocks.)
Force Place (Allow placement of all blocks, anywhere.)
No Updates (Don't send block updates)
Bulldozer (Quickly break blocks)
Gamemode switcher (Also unbound by default!)
Switch between Creative, Survival & Spectator with keybinds. These are also unbound by default.
How to use in Multiplayer
In order to function, Gimble needs to be installed on the Server.
Gimble will disable all modifications on the client, if it cannot find itself on the server.
People without Gimble may still join servers with Gimble installed.
There is no permission system (yet).