If you're interested in audiobooks too, https://libro.fm/ is DRM-free.
Greg Egan's books are on Smashwords, which is DRM-free. Most of them have the first chapter available on his website, which is good because some of it is REALLY hard sci-fi. I chipped a tooth reading Dichronauts (metaphorically speaking). Scale is more accessible. Diaspora is my favorite.
Thanks! How's the quality on the rest of the website? Many books just look like sloppy erotic novels...
Oh wow, I just now visited the rest of Smashwords, and yeah, it looks like mostly cheap romance. I've already read a lifetime supply of that as a kid, from fanfiction.
Cory Doctorow sells his books DRM-free (e-book and audiobook) on his webpage. Some of them are even pay-what-you-want.
It's always the sci-fi authors haha
He also writes non-fiction. You might be familiar with the term "enshittification". He is the author who coined that term.