The best alternatives to slalert! are Notify, Troops, and Lighthouse. If these 3 options don't work for you, we've listed a few more alternatives below.
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AssemblyAI— Speech-to-Text API with superhuman accuracy
Whenever your Startup gets mentioned on Twitter, Facebook, Instagram, Youtube, Google+, Blogs, Forums, News, Reddit, Medium, Hacker News and Product Hunt. Get Notified on Slack or HipChat.
Troops.ai provides salesforce automation platform that gives real-time transparency around salesforce information. It serves as a Slackbot for sales team.