Project Zomboid [Steam, GOG], the zombie survival sandbox game has two new big features in their beta right now. A Factions system to bring survivors together and VOIP chat for survivors near each other.
Essentially, the PZ Factions system is like having your own Clan or Guild when playing online. It's a pretty nice idea, and it will be fun to see where the go with it.
Then we have the VOIP system. It's not a map-wide VOIP, so you will only be able to chat with survivors that are near your location.
See the details on this forum post. To be able to try it out, you need to be on their IWBUMS beta branch, which is opt-in on Steam.
Have you tried it out recently?