Most blockers are browser extensions that are too easy to bypass, or bloated desktop apps with annoying dashboards.
I built LockIn. It's a proprietary system-level blocker that edits /etc/hosts directly with zero latency. The twist is that you don't interact with an app; you control it entirely via text messages with poke (or other AI assistants). You tell your AI agent to focus, and it locks down your system.
It runs as a lightweight app and connects directly to your laptop (phone app blocking in the future too hopefully). You can check it out at lockinmcp.com.