Looking for a SelfControl alternative?
SelfControl is a well-liked free Mac app that blocks websites for a set period. If it does what you need, it's a good tool.
FlowShizz covers the same ground and adds the thing people most often ask for: it blocks apps as well as websites.
What FlowShizz adds
Blocking apps, not just sites. Slack, a game, a messaging app — if it's open during a block, FlowShizz closes it.
Saved presets, so you don't rebuild your list every time.
Recurring schedules, so blocks start on their own at the hours you choose.
An optional Pomodoro timer.
What's the same
Both are free. Both keep working once a block has started. Neither asks you to make an account.
If you also use an iPhone
FlowShizz has a free iPhone app that blocks apps and websites there too. A one-off £4.99 purchase links the two, so one tap blocks both. There's no subscription.
Requirements
macOS 13 Ventura or later, Apple silicon and Intel. Free download from this site.