I like something called littr.me, single community link aggregator (like HN) but federates, so you get the interaction between communities but each community is sovereign, free to isolate itself as it pleases.
But it isn't about "a replacement for reddit." It is about finding communities online you want to engage in and engaging. Forums, non-federated aggregators (like HN), chatrooms all suffice. The trick is to avoid a one stop shop for communities.