Koa11y is a desktop app which scans any specific web page for accessibility issues.
The program looks for a wide range of problems: missing image Alt attributes, missing titles, colour contrast issues, lengthy ALTs, poorly designed forms, and anything else that doesn't play nicely with accessibility software and APIs.
Koa11y is aimed at professionals, not the casual user. The reports are comprehensive and detailed, organising any issues into three categories: Errors (fix now), Warnings (take a look), and Notices (suggestions). Take a look at a sample report here.
While there's a lot of web analysis going on here, the program itself is very simple. At a minimum, you might just enter a URL, specify an output folder and click Run. An HTML report file is produced within seconds.
If HTML doesn't suit your needs, the program can save reports in CSV, JSON, XML and Markdown.
Experts can also validate the page using several standards. WCAG2AA is the default; WCAG2A is a little more lenient, WCAG2AAA a little more strict; and Section 508 is a separate US government standard.
Koa11y can detect and highlight a stack of web accessibility issues, but the program won't be for everyone. The reports are technical, there's no flexibility in the analysis (check this rule, ignore that one), and there's no option to scan an entire site-- it's the specified URL only.