What are some alternatives?
When comparing Crawl Center and phpSitemapNG, you can also consider the following products
Screaming Frog SEO Spider - The Screaming Frog SEO Spider is a small desktop program (PC or Mac) which crawls websites’ links...
DYNO Mapper - Create Sitemaps with the DYNO Mapper Visual Sitemap Generator.
Pulno - SEO Audit and Website Analysis. Pull up your SEO.
XML-Sitemaps.com - Free Online Google Sitemap Generator.
ContentKing - The world's only Real-time SEO Auditing and Content Change Tracking suite.
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.