Yes, both Slab and Trello offer a Free Trial.
Slab is designed for Medium Business and Small Business.
Trello is designed for Individuals, Freelancers, Large Enterprises, Medium Business and Small Business.
Pricing for Slab Starts at $35/Month when Billed Yearly whereas for Trello Starts at $5/User/Month when Billed Yearly.
Some top alternatives to Slab includes Archbee, GitBook, Zoho Wiki, Drupal Wiki, LearnLode Enterprise, Matterial, TWiki, Wiki Valley, GoGoWorx and Kbee.
Some top alternatives to Trello includes Quickbase , Smartsheet, ClickUp, Zoho Projects, Freshbooks, Jira, Basecamp, Wrike, monday.com, Asana, Teamwork, ProjectManager.com, Microsoft Project, Worksuite, Trackboard, Quick Base, Todoist, Resource Guru and Height.