Cartridge Builder (FGLide) was developed for extracting existing data (modules, derived metrics, rules, agents, etc) from an existing Foglight Management Server for the purpose of transferring the information including environment customizations to another Foglight Management Sever via a cartridge. We use it often for syncing configuration modifications between multiple Foglight Management Servers to reduce having to enter configuration changes manually.
Custom metrics is not an option to be included using Cartridge Builder, custom script agent can be used for that purpose.
Alternative Help:
Go to Cartridge Builder link on the Development Tools dashboard. Once there, select the Help on the Action Pane to view the Developing Foglight Cartridges | Dashboard Support Guide.
Steps 1 - 4 under KB article 185435 discuss installing the Cartridge Builder cartridge.
There is a document attached that could help on basic use of this cartridge.