The best alternatives to Parties for WWDC are Raycast, WWDC for macOS v5, and WWDC Together. If these 3 options don't work for you, we've listed a few more alternatives below.
What do you think of Parties for WWDC?
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WWDC Together is a free place to watch and hangout during WWDC. We can now view upcoming and previous sessions via modern playback, with a chatroom for each session. Hope this provides a similar WWDC vibe.