Alternatives to Mibbit for all platforms with any license

Thunderbird

Thunderbird is a free, open source, cross-platform e-mail, news and instant messaging client. The project strategy is modeled after Mozilla Firefox.

Free Open Source Mac Windows Linux BSD PortableApps.com ... Haiku
Extensible by Plugins/Extensions Built-in RSS reader Calendar integration Support for IMAP ... Multiple Account support Open Source apps SMTP integration Add-ons Built-in Calendar Categories Customizable Delivery reports Encryption Extensible by Plugins/Extensions Free API Gmail integration Google Calendar integration Import from Google Reader HTML Compose Integrated Chat Integrated Password Manager Integrated Web Browser Legacy addons support Open source software Export to OPML Import feeds from OPML Protected by Password POP3 Support Portable Secure File Sharing Tabbed interface Support for Themes Add a feature

1920 Like
HexChat

HexChat is an IRC client based on XChat for Linux , but unlike XChat it’s completely free for both Windows and Unix-like systems. HexChat was...

Free Open Source Mac Windows Linux BSD PortableApps.com ... Xfce MacPorts XQuartz
Portable Add a feature

188 Like
mIRC

mIRC is a popular Internet Relay Chat client used by millions of people, and thousands of organizations, to communicate, share, play and work with each other on IRC...

Commercial Windows
Chat Colored Text Add a feature

86 Like
irssi

Irssi is a terminal based IRC client for UNIX systems. It also supports SILC and ICB protocols via plugins.

Free Open Source Mac Windows Linux BSD Cygwin
Chat Add a feature

75 Like
KVIrc

KVIrc is a free portable IRC client based on the excellent Qt GUI toolkit. KVirc is being written by Szymon Stefanek and the KVIrc Development Team with the contribution...

Free Open Source Mac Windows Linux BSD PortableApps.com
Chat Portable Add a feature

39 Like
XChat for Linux

XChat is an IRC chat program for both Linux and Windows. It allows you to join multiple IRC channels (chat rooms) at the same time, talk publicly, private one-on-one...
- Discontinued The program is no longer updated. Last version, 2.8.8, released in May 2010, can be still downloaded from the official website.
Free Open Source Windows Linux
Chat Add a feature

103 Like
ZeroChat

An IRC-like internet chatroom hosted on ZeroNet, a distributed network. 0rc is a fully distributed website, and messages are shared through peers using the ZeroNet...

Free Open Source Mac Windows Linux Web Self-Hosted ... Python JavaScript ZeroNet
Decentralized Distributed Add a feature

10 Like
IRCCloud

IRCCloud is an IRC client with a future. Stay connected, chat from anywhere, and never miss a message.

Freemium Web Android iPhone
Offline logs Add a feature

15 Like
Kiwi IRC

A hand-crafted IRC client that you can enjoy. Designed to be used easily and freely. More friendly than other webirc clients giving the general public an easy option to...

Free Open Source Web Self-Hosted Chrome
Chat Preconfigurable auto-connect Add a feature

20 Like
Shout

What is it? Shout is a web IRC client that you host on your own server. What features does it have? * Multiple user support * Stays connected even when you close...
- Discontinued Shout's development has stopped early 2016 and replaced by its official community fork: http://alternativeto.net/software/the-lounge/ . See https://github.com/erming/shout
Free Open Source Web Self-Hosted
Chat Add a feature

12 Like
Konversation

Konversation is an IRC client which gives you speedy access to Freenode network's channels, where you will find support for most distributions.

Free Open Source Linux
Chat Add a feature

22 Like
Textual

Textual is the world's most popular application for interacting with Internet Relay Chat (IRC) chatrooms on OS X. Textual includes two elegantly designed light...

Commercial Mac
User friendly Add a feature

17 Like
Chatzilla

ChatZilla is a clean, easy to use and highly extensible Internet Relay Chat (IRC) client, built on the Mozilla platform, which provides all the usual features: multiple...

Free Open Source Mac Windows Linux SeaMonkey Firefox
Chat Add a feature

19 Like
Qwebirc

qwebirc is a web based AJAX IRC client.

Free Open Source Windows Linux BSD Self-Hosted
No features added Add a feature

7 Like
Colloquy

Traditionally, chat clients on the Mac have been anything but glamorous. Colloquy is an advanced IRC, SILC & ICB client which aims to fill this void. By adhering to...

Free Open Source Mac
Chat Add a feature

34 Like