If HydraFlix is just temporarily down
Fmovies is the closest match to HydraFlix in terms of how it works, what it offers, and the kind of experience you get. It has a similarly large library, supports both movies and TV series, and does not require registration. If you just need something that works the same way while HydraFlix is unavailable, Fmovies is the natural first stop.
Soap2Day is worth bookmarking too, particularly if you watch a lot of TV series. Its episode organisation and autoplay are slightly better handled than most alternatives, and it tends to be more stable day-to-day than some of the others.
Tip: Bookmark two or three alternatives rather than one. Free streaming sites go through periods of downtime and domain changes — having backups means you are never stuck waiting for one specific platform to come back online.
If you want something fully legal
Tubi and Pluto TV are the two legitimate picks here. Both are owned by major media companies, both carry proper licensing deals, and neither is going anywhere. The downside is the library — you are not getting the latest releases, and the selection skews toward catalogue content. But if you are catching up on older films or just want something to watch without thinking too hard about legality, either of these works well.
Tubi is better for on-demand watching. Pluto TV is better if you want the feel of regular TV — channels running continuously, something always on, no decision required.
What to watch out for with free streaming alternatives
The alternatives listed here are the ones worth using. But the free streaming space also has a lot of sites that are not worth your time — sites that are either barely functional, loaded with malware-adjacent ads, or simply abandoned mirrors of something that used to exist. A few things to look out for when trying a site you have not heard of: if it asks you to sign up before showing you anything, leave. If it immediately prompts you to download a file or install something, leave. If the only way to close a pop-up is to click something on it rather than an X button, close the whole tab.
The sites on this page have been in the space long enough that their general behaviour is well documented. That does not make them perfect, but it does mean you know roughly what to expect.