Here is a list of all topics with brief descriptions:

aalib
audio	Sounds on mixer channels and PCM streaming for the EE, with an IOP driver on the SPU2
Error codes	Positive constants; functions return them negated
Lifecycle and global settings
Stream	PCM playback for music and video audio
Sounds	ADPCM sounds kept in SPU2 memory
Channels	Mixer channels 0 to 23 that play sounds
Effects	The SPU2 reverb and delay
Effect presets	Values for audio_effect_set_preset()
Contexts	The audio library on an explicit context instead of the default one
audsrv-compat	The audsrv API on top of the audio library
Error codes	Functions return them negated; audsrv_get_error() returns the last one as a positive value
Stream
CD audio	Not supported. Every function returns -AUDSRV_ERR_NO_DISC
ADPCM samples	Sounds played on channels 0 to 23
dmakit
freetype
gskit-toolkit
gskit
hash
hdd	HDD library functions
input	Input library
inputx	Input library
ioptrap	IOP exception handler and breakpoint support; other IOP modules hook it through set_exception_handler
libid3tag
libjpeg_ps2_addons
libmad
libpng
libsnd2
libtap
lua
mmceman
ppctty	IOP module that redirects printf output to the PowerPC UART of DECKARD consoles; unloads itself on other models
rspu2drv
sdr	Definitions for libsdr on the EE
siocookie
smbman	Imports and definitions for ps2ip. Real, verbatim upstream header (iop/tcpip/tcpip/include/ps2ip.h) - declares the IOP-side ps2ip.irx module's real exported symbols (lwip_, ps2ip_, pbuf_, netif_, tcpip_ prefixed - real dynamic IRX imports, resolved by the IOP kernel at module-load time via imports.lst, not by ps2build/iopfixup at build time) for a consumer like smbman that gets loaded alongside a running ps2ip.irx. sdk-core does not yet ship a real ps2ip.irx (only the EE-side lwip build, core/ps2ip, and the SIF-RPC-based core/ps2ips client - a genuinely different, third architecture from this IOP-dynamic-import one) - deliberately deferred per direct decision, so this package builds real and clean but needs a real ps2ip.irx present at runtime to actually load. Placed here (not core/common) since smbman is its only consumer right now; move to a shared location if/when the real IOP tcpip.irx port lands and other IOP-dynamic-import consumers show up
subfile
udptty	IOP tty driver that sends console output over UDP; needs the IOP-side ps2ip module at runtime
unzip
zlib