What are some alternatives?
When comparing GlooMaps and phpSitemapNG, you can also consider the following products
DYNO Mapper - Create Sitemaps with the DYNO Mapper Visual Sitemap Generator.
XML-Sitemaps.com - Free Online Google Sitemap Generator.
A1 Sitemap Generator - A1 Sitemap Generator has been in active development and sold since 2005.
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.
FlowMapp - UX planning tool for creating a visual sitemap
VisualSitemaps - Autogenerate visual sitemaps in seconds.