weechat + wee-slack.py works quite well.
I'm so used to using wee-slack that I try to use commands like "s/" when I use the web browser interface (which doesn't work).
One thing I wish wee-slack had (and I haven't updated in months, so it may by now) is the ability to download files attached to messages without opening the URL to webslack. That, and occasionally silent failure to display long notes attached to messages, are the only major hurdles I encounter with wee-slack on a regular basis.