Syncthing — Syncthing is a continuous file synchronization program. It synchronizes files between two or more computers in real time, safely protected from prying eyes.
Stingle Photos — Stingle Photos is a convenient, easy to use Gallery/Camera application with Backup and Sync functionality for your photos and videos which seamlessly provides strong security, privacy and encryption.
pigallery2 — A fast directory-first photo gallery website, with rich UI, optimized for running on low resource servers.
Photoview — Photoview is a simple and user-friendly photo gallery that's made for photographers and aims to provide an easy and fast way to navigate directories, with thousands of high-resolution photos.
LibrePhotos — A self-hosted open source photo management service.