It has been called Lingo → by the developer Johnathan Clough [the link takes you to the download page on the Mac AppStore].
As of today my preferred IRC client on OS X has been Colloquy, an old acquaintance of mine after my X-Chat day ended switching to Mac in 2006. Colloquy has been a reliable, open source project that never failed me (almost) in these 8 years.
More recently I’ve had the chance to also evaluate Textual… which I did not like at all!!! Being a paid app my expectations were probably a bit too high… Both the gratis apps Colloquy and Lingo – to my usage – have proved to be more feature rich, both in terms of customization and offered functionalities.
Lingo, since my epiphany of it last monday, has been running smoothly and without a single hitch on two of my Mac connected on the FreeNode servers and logged on seven channels (a couple with a discrete amount of daily traffic). So here I am singing its praises!