libnfnetlink is the low-level library for netfilter related kernel/userspace communication. It provides a generic messaging infrastructure for in-kernel netfilter subsystems (such as nfnetlink_log, nfnetlink_queue, nfnetlink_conntrack) and their respective users and/or management tools in userspace.

This library is not meant as a public API for application developers. It is only used by other netfilter.org projects, such as libnetfilter_log, libnetfilter_queue or libnetfilter_conntrack.

ulogd is a userspace logging daemon for netfilter/iptables related logging. This includes per-packet logging of security violations, per-packet logging for accounting purpose as well as per-flow logging.

Xtables is used to set up, maintain, and inspect the tables of IP
packet filter rules in the Linux kernel.

Xtables-addons is the successor to patch-o-matic(-ng). Likewise, it
contains extensions that were not, or are not yet, accepted in the
main kernel/iptables packages.

libdbi implements a database-independent abstraction layer in C, similar to the DBI/DBD layer in Perl. Writing one generic set of code, programmers can leverage the power of multiple databases and multiple simultaneous database connections by using this framework.

sshfp generates DNS SSHFP records from SSH public keys. sshfp can
take public keys from a knownhosts file or from scanning the host's
sshd daemon. The ssh client can use these SSHFP records if you set
"VerifyHostKeyDNS yes" in the file /etc/ssh/ssh_config.

Brotli is a generic-purpose lossless compression algorithm that compresses data
using a combination of a modern variant of the LZ77 algorithm, Huffman coding
and 2nd order context modeling, with a compression ratio comparable to the best
currently available general-purpose compression methods. It is similar in speed
with deflate but offers more dense compression.

ngx_brotli is a set of two nginx modules:

ngx_brotli filter module - used to compress responses on-the-fly,
ngx_brotli static module - used to serve pre-compressed files.