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?
Haggle — A CTA buyers want to click, when they aren't ready to demo
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.