Users

Botan has been used in all kinds of projects. Feel free to add a link and description of yours if you like.

Open Source Software

strongSwan IPsec software
PowerDNS DNS server
Biboumi is an IRC gateway for XMPP.
RNP is an OpenPGP library.
NeoPG the "multiversal crypto engine", is an opinionated fork of GnuPG written in C++
ISC KEA DHCP server
Kaa is an open-source IoT platform
libQtShadowsocks, shadowsocks-qt5 and shadowsocks-deepin are interfaces to the shadowsocks proxy system
SoftHSM is an software PKCS #11 token
Qt Creator, an IDE for building Qt applications.
QSsh is a SSH/SFTP library
QOwnNotes is a notepad tool
Monotone distributed version control system
cppssh is a C++11 SSH library
QCA, the Qt Cryptographic Architecture (part of KDE4) uses parts of botan as an embedded crypto provider
TCHead is a utility for analyzing TrueCrypt volume headers.

Rohde & Schwarz Cybersecurity, a German security software company, uses Botan in some of its products.
One-Way Automation's OPC UA SDK
Cisco Communicator Desktop and StealthWatch Enterprise
Rockwell Automation
Mazda Infotainment system
Panasonic UConnect Infotainment system
IBM Netezza
Bosch Video Management System
PSPDFKit for iOS and Android is a PDF toolkit used in dozens of mobile applications.
Kodak Alaris Capture Pro
VMware AirWatch
Cyclonis Password Manager
EnFocus PDFReview
One Identity Safeguard for Privileged Sessions
Silverlock is a password management tool for OS X
1qbit SDK
Shimmercat HTTP/2 server
Balabit Shell Control Box
Flume, a tool to securely and accurately move your distributed data at unprecedented speeds, uses Botan for encryption and hashing.
CA Agile Requirements Designer
Hitman Pro is a malware scanner for Windows.
Flying Lab Software, a Seattle based game developer, uses botan as a part of their user authentication process.
CryptoTE is a text editor with integrated strong cryptography.
TextEgg is an encrypted document editor.