Here are the data structures with brief descriptions:

cal_table	Calibration table struct
chan_list	Memory channel list definition
channel	Channel structure
channel_cap	Channel capability definition
confparams	Configuration parameter structure
ext_list	Extension attribute definition
filter_list	Filter definition
freq_range_list	Frequency range
gran	Level/parm granularity definition
hamlib_port_t	Port definition
rig	The Rig structure
Rig
rig_callbacks	Callback functions and args for rig event
rig_caps	Rig data structure
rig_list
rig_state	Rig state containing live data and customized fields
RigException
rot	This is the master data structure, acting as a handle for the controlled rotator
rot_caps	Rotator data structure
rot_list
rot_state	Live data and customized fields
Rotator
tuning_step_list	Tuning step definition
value_t	Universal approach for passing values