Here is a list of all files with brief descriptions:

[detail level 12]

▶ c2s
address.c
authreg.c
bind.c	Xmpp resource binding
c2s.c
c2s.h
main.c
pbx.c	PBX integration
pbx_commands.c	PBX integration commands interpreter
sm.c
▶ mio
mio.c
mio.h	Mio - manage i/o
mio_epoll.c
mio_epoll.h
mio_impl.h
mio_kqueue.c
mio_kqueue.h
mio_poll.c
mio_poll.h
mio_select.c
mio_select.h
mio_wsasync.c
mio_wsasync.h
▶ router
aci.c
filter.c
main.c
router.c
router.h
user.c
▶ s2s
db.c
in.c
main.c
out.c
router.c
s2s.h
util.c
▶ sm
aci.c	Access control manager
dispatch.c	Packet dispatcher
feature.c	Feature registration
main.c	Initialisation
mm.c	Module manager
mod_active.c	Active user management
mod_amp.c	Advanced Message Processing (JEP-0079) module
mod_announce.c	Announce (broadcast) messages
mod_deliver.c	Packet delivery
mod_disco.c	Service discovery
mod_echo.c	Message echo
mod_help.c	Forward messages to administrators
mod_iq_last.c	Last activity
mod_iq_ping.c	Xmpp ping
mod_iq_private.c	Private xml storage
mod_iq_time.c	Entity time
mod_iq_vcard.c	User profiles (vcard)
mod_iq_version.c	Software version
mod_offline.c	Offline storage
mod_pep.c	XEP-0163: Personal Eventing Protocol
mod_presence.c	Presence tracker driver
mod_privacy.c	XEP-0016 Privacy Lists and XEP-0191 Simple Comunications Blocking
mod_roster.c	Roster managment & subscriptions
mod_roster_publish.c	Roster publishing
mod_session.c	Session control
mod_status.c	Status info management
mod_template_roster.c	User auto-population - roster
mod_vacation.c	Vacation messages
mod_validate.c	Packet validator
mod_verify.c	Verify users using e-mail
pkt.c	Packet abstraction
pres.c	Presence tracker
sess.c	Session management
sm.c	Stream / io callbacks
sm.h	Data structures and prototypes for the session manager
user.c	User management
▶ sx
ack.c
callback.c
chain.c
client.c
compress.c
env.c
error.c
io.c
plugins.h
sasl.c
sasl.h
server.c
ssl.c
sx.c
sx.h
websocket.c
▶ util
access.c
base64.c
base64.h	Base64 encoding
config.c
crypt_blowfish.c
crypt_blowfish.h
datetime.c
datetime.h	ISO 8610 / JEP 82 date/time manipulation
hex.c
inaddr.c	Object like wrapper around struct sockaddr_storage
inaddr.h
jid.c
jid.h	Jabber identifiers
jqueue.c
jsignal.c
log.c
log.h	Logging functions
md5.c
md5.h
misc.c
misc.h	Miscellaneous utilities
nad.c
nad.h	Not A DOM
pool.c
pool.h
pqueue.c
pqueue.h	Priority queues
rate.c
serial.c
sha1.c
sha1.h
stanza.c
str.c
uri.h	Common URIs
util.h
util_compat.h	Define the structures that could be missing in old libc implementations
xdata.c
xdata.h
xhash.c
xhash.h	Hashtables