Yes, both GitHub and ZenHub offer a Free Trial.
GitHub is designed for Freelancers, Large Enterprises, Medium Business and Small Business.
ZenHub is designed for Large Enterprises, Medium Business and Small Business.
Pricing for GitHub Starts at $4/User/Month whereas for ZenHub Starts at $8.33/user/month when yearly.
Some top alternatives to GitHub includes LiveCode, Codeanywhere, Visual Studio IDE, CodeinCloud, GitLive, Microsoft Azure, GitLab, CodeSee and Bitbucket.
Some top alternatives to ZenHub includes Quickbase , Smartsheet, ClickUp, Zoho Projects, Jira, Trello, Wrike, Asana, Teamwork, Kanbanize, Trackboard, Quick Base, Zenkit Projects, Height, Yodiz and Worktez.