Yes, both OmniFocus and ClickUp offer a Free Trial.
OmniFocus is designed for Large Enterprises, Medium Business and Small Business.
ClickUp is designed for Freelancers, Large Enterprises, Medium Business and Small Business.
Pricing for OmniFocus Starts at $9.99/Month whereas for ClickUp Starts at $7/User/Month when yearly.
Some top alternatives to OmniFocus includes Todoist, Wrike, Smartsheet, Asana, ProWorkflow, nTask, Taskworld, TickTick, Today, MeisterTask, ClickUp and StickyList.
Some top alternatives to ClickUp includes Basecamp, Trello, TeamGantt, Asana, Teamwork, ProjectManager.com, ProWorkflow, nTask, Todoist and Height.