Local playback, broad format support, subtitle and audio-track switching, plus casting to other devices. A few of each.
A native, open-source network diagnostics app for macOS with Wi-Fi analysis built in. It surveys nearby wireless networks, signal strength and channel usage, assesses connection quality and helps diagnose Bluetooth and network issues. It suits troubleshooting Wi-Fi interference and tuning home or office networks.
Free
VLC media player - plays everything, runs anywhere. Code here: https://code.videolan.org/videolan/vlc
Free
A command-line media player. Built on ffmpeg, it plays almost any audio or video format with subtitles, can be scripted to control playback and processing, and extends through config files and Lua scripts. It has no interface of its own but works with front ends, which suits precise control or embedding playback in automation.
Free
A free-software media system providing the server backend and API. It organises films, series and music, streams and transcodes to a range of clients, and supports multiple users, permissions and metadata scraping. It suits people building a home media library instead of relying on a commercial streaming service.
Free