We use ZNC for bouncing services (irc-bouncer:6676). Apparently you add new users like this. This amounts to:-

• Use znc –makepass to generate a sha256 password hash
• Ignore their whining about not editing the config and add:

<User frank>
      Pass = sha256#password#salt#
      Nick = frank
      AltNick = frank_1
      Ident = frank
      RealName = New User
      QuitMsg = *poof*
      StatusPrefix = *
      Buffer = 100
      KeepBuffer = true
      MultiClients = true
      BounceDCCs = true
      DenyLoadMod = false
      Admin = false
      DenySetVHost = false
      DCCLookupMethod = default
      TimestampFormat = [%H:%M:%S]
      AppendTimestamp = false
      PrependTimestamp = true
      TimezoneOffset = 0.00
      JoinTries = 10
      MaxJoins = 5
      IRCConnectEnabled = true

      Server = irc.wormnet.eu 6667
</User>

• # killall -HUP znc
• Login to the bouncer, supplying nick and password

As of 2020, ZNC is now listening with SSL/TLS on port 6697.

Browsers might not enjoy connecting to “naughty” ports, and might need hidden knobs tweaking, eg network.security.ports.banned.override on Firefox.

There's a difference between a nick password and a connection password. Some clients, like Thunderbird, seem not to believe in the sensibilities of the latter–although they left hidden knobs messenger.account.account0.options.username and messenger.account.account0.options.serverPassword (browse about:config and replace the 0 with the relevant number).

Bitlbee is an IRC → Jabber/Twitter/ICQ/Whatever-else gateway, running on port localhost:6666.

• A reasonable terse guide to getting going: https://help.ubuntu.com/community/Bitlbee
• More in-depth: http://wiki.redbrick.dcu.ie/mw/Bitlbee

You can auto-connect to bitlbee on startup with these sorts of things in your config:-

servers = (
  {
    address = "localhost";
    chatnet = "bitlbee";
    port = "6666";
    use_ssl = "no";
    ssl_verify = "no";
    autoconnect = "yes";
  },

chatnets = {
  bitlbee = { type = "IRC"; };

channels = (
  {
    name = "&bitlbee";
    chatnet = "bitlbee";
    autojoin = "yes";
    autosendcmd = "/msg root identify my-secret-identity";
  },

There may be a better way to do the last bit, but meh.