What are some alternatives?
When comparing phpSitemapNG and FlowMapp, you can also consider the following products
DYNO Mapper - Create Sitemaps with the DYNO Mapper Visual Sitemap Generator.
Really Good UX - A library of screenshots for UX inspiration
XML-Sitemaps.com - Free Online Google Sitemap Generator.
VisualSitemaps - Autogenerate visual sitemaps in seconds.
WonderWebWare Sitemap Generator - Sitemap Generator is freeware program that will help you to automatically generate site maps for google, bing and yahoo in their respective file formats.
GlooMaps - Create your visual sitemap on the go - easy peasy