FlowMapp - FlowMapp is a UX planning tool for creating visual sitemaps and user flow.
LinkChecker - LinkChecker is a free, GPL licensed website validator.
Octopus.do - Build your website structure in real-time and rapidly share it to collaborate with your team or clients. Start prototyping websites or apps instantly.
Pulno - SEO Audit and Website Analysis. Pull up your SEO.
DYNO Mapper - Create Sitemaps with the DYNO Mapper Visual Sitemap Generator.
Checkbot - Checkbot will boost the SEO, speed and security of your site by checking you're following 50+ web best practices. Browser extension with free and paid plans.