Nintex Workflow is described as 'simple, powerful tool for process automation. The intuitive, browser-based drag-and-drop workflow designer lets you tackle everything from a specific task in a single department to complex, company-wide procedures' and is a Workflow Automation App in the category. There are six alternatives to Nintex Workflow for a variety of platforms, including Windows, Online / Web-based, iPhone, iPad and SaaS. The best alternative is Fluix. Other great apps like Nintex Workflow are Flowingly (Paid), Logiak (Paid), ClaySys AppForms (Paid) and kenaflow (Paid).
kenaflow is a Business Automation Engine that leverages PowerShell for workflow creation and execution. It works well with SharePoint (Online/2013/2016/2019) and Mail-Inboxes. It runs on Windows OS. A cloud offer (SaaS) is coming soon.