Converse is an editor for .fco (Font Converse) files from Sonic Unleashed and Sonic Generations.
Sonic Team called this file format "Font Converse", which is where the "fco" extension comes from.
Converse Editor can currently open any fco and fte file from Sonic Unleashed and Sonic Generations, some files from the Sonic Unleashed Preview Builds will not work, as they were older internal revisions of the format.
Thanks to Hedgeturd for explaining everything related to fco and fte files!