Mac: Spoken Content with Premium voices (free)
In System Settings → Accessibility → Spoken Content, choose Manage Voices and download an Enhanced or Premium voice (Zoe, Ava and others; a few hundred MB each). Turn on Speak selection, and OptionEsc reads whatever you've selected in any app, offline.
Good: free, built in, surprisingly natural. Not so good: no audio files or audiobooks, no PDF reader of its own, and some apps on macOS Tahoe have been reported to skip Premium voices.
Windows 11: Narrator's natural voices (free)
Windows 11 can download natural voices such as Jenny, Aria and Guy, and once installed they work offline. The catch: only Narrator, the screen reader, uses them, and Narrator reads everything you move to, which is a lot for simply reading a document. Our guide covers what works and what doesn't.
Good: free and natural. Not so good: Narrator only; Edge's Read Aloud has natural voices too, but those are online.
Balabolka (free, Windows)
A long-standing free reader that opens documents and saves them as MP3, WAV, OGG and other formats, with any voice installed in Windows. Alternatives to Balabolka.
Good: free audio files, lots of control. Not so good: Windows' built-in voices for it are the older, robotic ones. Natural voices need the unofficial NaturalVoiceSAPIAdapter, which its own author calls a hack, and which may not work with the newest Windows 11 voices.
Piper and Kokoro (free, open source)
Two neural voice engines that run on an ordinary processor. Piper has many voices in dozens of languages and is very fast; Kokoro sounds more natural in English and a handful of other languages.
Good: free, natural, offline. Not so good: mostly command-line tools or small community apps; no voice cloning; you put together the reading and file-saving parts yourself.
NaturalReader desktop (paid once)
The desktop version of NaturalReader is sold once: Personal is $99.50 with two natural voices and MP3 saving, for one computer. Extra voices cost $39.50 each, and commercial use of the audio needs a separate licence. How it compares.
Good: a familiar, polished document reader. Not so good: more expensive than it looks once you add voices, and check which of its voices work without the internet before you buy.
VoicedByMe ($30 once, Windows and Mac)
Natural AI voices that run on your own computer: 70 ready-made voices, or your own cloned from twenty seconds of talking. Select text in any app and press CtrlAltR; open PDF, EPUB and Word files with highlighting; make audiobooks with chapters; read text in pictures; no word limits.
Good: natural voices everywhere, your own voice, audiobooks, all offline. Not so good: eight languages only; Windows 10 and 11 and Macs with Apple silicon only; without a recent graphics card it's slow for live reading; no phone app.