In 1998, Congress amended the Americans with Disabilities Act and added Sections 504 and 508 to the statutes. Section 508 codifies the requirements to make a web site "accessible" to people with disabilities and remove the barriers to access inherent in most modern information technology. In light of that, I have tried to program this site to meet those requirements. At the same time, the only pages that give access to this page are written to the html5 standard that exists as of July, 2016.
In January 2017 Congress passed a rewrite of Section 508 to bring it up to date and achieve parity with the W3C's WCAG 2.0 AA specification. That update is scheduled to take full effect in January 2018. In my day job as a USFS Section 508 validator I need to come up to speed on implementing those specs myself, so this website is my guinea pig. One of the first things I've had to remove were the AddThis sharing buttons: AddThis engineering told me straight up they don't test anything for accessibility and have no plans to. I have a query in with Google's AdSense engineers to see where they're at re: accessibility but a lifetime ago I was intimately connected with Google for a number of years and accessibility was not in their playbook back then. Going by their ad code, it's still not, although they seem to have gotten it in various other of their initiatives...
Most modern browsers are html5 compliant and the site should render fully as it was meant to (although programming for all the various flavors of Internet Explorer is still an adventure of dubious value - thankfully Microsoft's Edge is a good step into the real world). Most screen readers should also have no problems with the site, although the newest versions are the ones I most recommend. As I am trying hard to write this to the standards, some features may not work well with some screen readers, particularly Screen Access To Go. But the newest versions of JAWS, NVDA, ChromeVox and VoiceOver will deliver the highest quality experience. ZoomText users will find pixelation in many of my images when expanded (happens when I compress images so as to not consume massive amounts of bandwidth and download time). For mobility impaired users I recommend Dragon NaturallySpeaking (part of which is the engine behind Apple's Siri). For the most part, the site is also responsive and should work reasonably well on most mobile devices.
Update: August, 2017: I think I have finally hit on the right mix of CSS selectors to bring this website fully up to snuff. Now I have to make a pass through every page on the site and do the actual code work. This is yet another case where building accessibility in from the first dream of a project is the best path to follow. Remediation after the fact is a time-and-effort-sucking bear. That said, the very first iteration of what has eventually become TheArmchairExplorer dates from 1998, before even CSS was available. The first version of Section 508 wasn't codified until 2001, when CSS 2 was just coming online.