Previously, twitterviewer.net, which had some annoying ads, was seemingly the only website of this type left.
But now twitterwebviewer is back. It doesn't have anywhere close to as many ads as twitterviewer does.
I don't know exactly when twitterwebviewer came back online. The owner of the website didn't announce on here or Reddit or seemingly anywhere else that he had restored the website, and I discovered the website was back a few hours ago by accident when I was doing a google search to get to the similarly named twitterviewer.
So now, even if you don't like all of twitterviewer's ads, there is an option to read Twitter without an account.