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

src
wget2-2.3.0
include
wget
wget.h
libwget
atom_url.c	URL extraction from Atom feed XML data
bar.c	Progress Bar Routines
base64.c	Base64 functions
bitmap.c	Functions for bitmap
buffer.c	Buffer management functions
buffer_printf.c	Buffer management functions
console.c	Console functions
dns.c	Functions for resolving names/IPs
dns_cache.c	Functions for DNS caching
error.c	Error functions
hash_printf.c	Hash convenience functions
hashfile.c	Hashing functions
hashmap.c	Hashmap functions
hpkp.c	HTTP Public Key Pinning (RFC 7469) routines
hsts.c	HTTP Strict Transport Security (RFC 6797) routines
io.c	I/O helper routines
ip.c	IP address functions
iri.c	Functions to work with URIs and IRIs
list.c	Circular doubly linked list routines
mem.c	Memory functions
net.c	Functions to work with TCP sockets and SSL/TLS
ocsp.c	Online Certificate Status Protocol (RFC 2560) routines
plugin.c	Plugin API for wget2
printf.c	Libwget printf functions
random.c	Random functions
robots.c	Robots Exclusion file parser
sitemap_url.c	URL extraction from Sitemap XML data
ssl_gnutls.c	Functions for establishing and managing SSL/TLS connections
ssl_wolfssl.c	Functions for establishing and managing SSL/TLS connections
stringmap.c	Stringmap functions
thread.c	Implementation of multi-threading basic functionality
utils.c	General utility functions
vector.c	Vector functions
xalloc.c	Memory allocation functions
xml.c	XML parsing functions