Slack2Peach is listed in:Connect to other messaging services
Messenger for WhatsApp, Telegram, Facebook, Slack & Hipchat
Slackline allows you to share Slack channels with other teams
Connect Slack to Skype, HipChat, and more.
Launch an online community with Mightybell you manage from Slack
Get the top posts from every Slack chat you're in.
Chat with Salesforce, Github, Mailchimp, Zendesk and 100 other apps.
One-click shared channel between 2 Slack teams
Chat with friends and teams on different IM networks (Currently Jabber and IRC)
Metachat makes it easy to deal with multiple Slack teams.
Easily update other teams about your work, through Slack.