Unity Web Player | SDF Toolkit
Available on the Unity asset store.
For more info, check out this topic.
You can now check out the documentation too.
And watch a demonstration video here.
For me, the colors are wrong in Safari when windowed. It's fine when going fullscreen, or with Chrome and Firefox.
This has to do with the color space. It's linear. If you can't get the colors right, try the gamma version.
Starting with Chrome version 42, you need to enable npapi via chrome://flags/#enable-npapi and restart the browser to get the Unity web player to work.