The base Lemmy site does allow that. It looks like every button should lead to sign up dialogs but doesn't. Just select a serer, then join a server, hit communities at the top and select all in the green menu. I don't know if it shows you everything but it does give many pages of topics and what server they are on.

The interface is not up to old.reddit standards but better than the modern reddit interface. I like that because there many servers, any popular topic will have a bunch of subs to choose from. Seems a bit sparse with subscriber numbers per community but if that grows, I could see it scratching the reddit itch...

The official Android app, Jerboa, doesn't require an account at all and defaults to anonymous browsing.