Was a breeze to setup on my file server (running Solaris for ZFS support; installing software is often unreasonably painful), actively updates its database as new files are added, and allows me to administer it remotely using the Serviio-Console GUI (e.g. to change the folders it scans, update profiles for clients, the directory structure it presents to clients)

For a barebones implementation, minidlna is a fantastic piece of software. I see MediaTomb recommended a lot, and I'm sure it's fantastic, but I've never managed to get it setup properly.