Note that the installer automatically downloads other dependencies and may require rebooting for scripting interfaces to work.
Latest development versions can be found at: dl.hexchat.net/hexchat/testing
Windows 10 users can get the latest version on the Windows Store.
Normally your distribution already has a package though it may be outdated.
Note these are community maintained repositories.
Note that these may not fully integrate into your system like traditional packages. They should be portable across multiple distributions though.
There are no longer maintained OSX builds.