Quassel IRCFor quite a while now I've been using Quassel IRC as my IRC client of choice. It is somewhat unusual as it is built on a client/core basis - there is a core that runs on a server and is permanently connected to IRC, and a client that connects to the core and lets you interact with IRC. In this way you can connect from anywhere and have access to all the backlog etc. It is still missing some quite major components (such as scripting, dcc, ...), but for now I like it enough to put up with that.

Another difference to most clients is that the backlog (and settings etc.) are held in a database and not in text files. This has both advantages and disadvantages - it is quicker for most operations, but less easy to e.g. search or publish logs (for searching see Quasselsuche. It requires that you run a web server, but works very well.). Quassel supports two database backends - SQLite and PostgreSQL of which the the default is SQLite. SQLite works just fine, but PostgreSQL scales better, so over time (and sooner if you are in a lot of/high traffic channels it can make sense to change. My SQLite database recently started approaching 1 GB, so I thought I'd switch and see how it went.