Flow offers Free Trial, but Rive does not.
Rive is designed for Individuals, Medium Business and Small Business.
Flow is designed for Large Enterprises, Medium Business and Small Business.
Pricing for Rive Starts at $14/User/Month when Billed Yearly whereas for Flow Starts at $6/User/Month when Billed Yearly.
Some top alternatives to Rive includes Harmony, Loading.io, Animation Desk, Adobe Animate, Adobe Character Animator, Spline, Stream Chat, Text Chat Animator, Flow and ImagickPro.
Some top alternatives to Flow includes Quickbase , Smartsheet, ClickUp, Zoho Projects, Wrike, TeamGantt, Teamwork, ProjectManager.com, Microsoft Project, ProWorkflow, Trackboard, TaskBranch, Quick Base, Height, Task Flow and Project Insight.