Here is a list of all documented files with brief descriptions:

[detail level 1234]

hamlib
include
hamlib
amp_state.h	Hamlib amplifier state structure
amplifier.h	Hamlib amplifier data structures
amplist.h	Hamlib amplifier model definitions
port.h	Hamlib port data structures
rig.h	Hamlib rig data structures
rig_state.h	Hamlib rig state data structure
riglist.h	Hamlib rig (radio) model definitions
rot_state.h	Hamlib rotator data structures
rotator.h	Hamlib rotator data structures
rotlist.h	Hamlib rotator model definitions
src
amp_conf.c	Amplifier Configuration Interface
amp_reg.c	Dynamic registration of amplifier backends
amp_settings.c	Amplifier function/level/parameter interface
amplifier.c	Amplifier interface
band_changed.c
cache.c
cache.h
cal.c	Calibration routines
cal.h
cm108.c	CM108 GPIO support
cm108.h
conf.c	Rig configuration interface
debug.c	Control Hamlib debugging functions
event.c	Event handling
event.h
ext.c	Extension request parameter interface
extamp.c	Amplifier extension parameters and levels interface
fifo.h
gpio.h
idx_builtin.h
iofunc.c	Generic file-based IO functions
iofunc.h
locator.c	QRA locator (Maidenhead grid square) and latitude/longitude bearing conversion interface
mem.c	Memory and channel interface
microham.h
misc.c	Miscellaneous utility routines
misc.h
mutex.h
network.c	Network port IO
network.h
par_nt.h
parallel.c	Parallel Port IO
parallel.h
register.c	Dynamic registration of backends
register.h
rig.c	Ham Radio Control Libraries interface
rot_conf.c	Rotator Configuration Interface
rot_conf.h
rot_ext.c	Rotator extension parameters and levels interface
rot_reg.c	Dynamic registration of rotator backends
rot_settings.c	Rotator functions/levels/parameters interface
rotator.c	Rotator interface
serial.c	Serial port IO
serial.h
serial_cfg_params.h
settings.c	Func/level/parm interface
sleep.c	Replacements for sleep and usleep
sleep.h
snapshot_data.h
sprintflst.h
token.h	Token definitions
tones.c	CTCSS and DCS interface and tables
tones.h
usb_port.c	USB IO
usb_port.h