Yes, both Guru and Slack offer a Free Trial.
Guru is designed for Large Enterprises, Medium Business and Small Business.
Slack is designed for Freelancers, Large Enterprises, Medium Business and Small Business.
Pricing for Guru Starts at $14/User/Month when Billed Yearly whereas for Slack Starts at $2.67/Month.
Some top alternatives to Guru includes GitBook, Zoho Wiki, KBPublisher, Drupal Wiki, LearnLode Enterprise, TWiki, Wiki Valley, GoGoWorx, HuForce and ProProfs Knowledge Base.
Some top alternatives to Slack includes Microsoft Teams, Glip, Google Chat, ChatWork, Dialog, Office Chat, imBee, Takle, SPACE Channel and Teamwork Chat.