Half-Life 2 co-op mod Synergy upgraded for the Half-Life 2 20th Anniversary Update

Synergy is a free mod for Half-Life 2 that allows you to play the Half-Life 2 series and many other singleplayer Source Mods cooperatively with friends. It was recently upgraded to support the Half-Life 2 20th Anniversary Update.

This is the first proper update to the mod since 2015, so it's quite a big one. It includes lots of enhancements, including better Steam Deck support! The developers mentioned they've been working on it for a long time, but they released it "sooner than we've planned as to resolve numerous breaking changes from Half-Life 2's recent large update".

Here's all the highlights of what's new and improved:

• Support for the Half-Life 2 20th Anniversary Update!
• Fixed numerous crashes like the infamous "unconnected" player bug and player models jittering.
• Significantly improved overall performance, especially with large player counts.
• Rebalanced numerous, rather absurd, map-specific difficulty spikes in the Half-Life 2 campaign.
• Fixed SteamVR starting when changing settings.
• Initial official native support for Steamdeck (UI still leaves a lot to be desired).
• Fixed various HUD issues introduced by Half-Life 2's Steamdeck update.
• Official support for Linux Dedicated Servers.
  • Requires steam client installed (e.g. `sudo apt install steam`).
• Added support for saved games.
  • Host can load a saved game and friends who join will be restored if they were connected at the time of the save.
  • Works on dedicated servers.
• Various map-specific (EDT) improvements throughout the Half-Life 2 campaigns.
• Fixed many level transition issues, particularly on backtracking maps.
• Steam Cloud support for settings and saved games.
• Steam Workshop support for dedicated servers.
• Steam Rich Presence support.
• Enabled spectator mode via console (jointeam 1)
• Players will spawn in a vehicle on airboat levels (coast levels TBD).
• Vehicles will no longer stop when the game autosaves.
• Added more player voice command lines from ep1.
• Fixed player viewmodels being invisible under some circumstances.
• Optimized networking for some entities like the Airboat.
• 'Use' key will now go through players to avoid blocking anything.
• Removed cheat flag from some useful commands/cvars.
• Added game content rating to unblock Synergy in Germany.
• Increased maximum player support from 10 to 32.
• Other changes lost in time.

What's next for it? They're working on "automatic networking and Steam friend lobbies" to make it easier to join up with friends without needing port forwarding, which they hope to have "ready in the near future".