In the big picture, all of them do.
Open source communities know the importance of diversity and had answers for all aspects of accessibility very early on. Fun fact: pure HTML has been accessible (and adaptive) from the very beginnings. If we don't mess it up with fancy requirements, it still can be.
Of course, when customers decide to value features over accessibility, it may happen that their final design is just as good as they allowed it to become. You must stress that you mean your project to be accessible in every aspect and you should be ready to "kill your darlings" (cute little things that simply go wild).
Accessible back-ends
A not so commonly known aspect is the accessibility of the CMS itself (in contrast to the rendered pages that are managed through the CMS. The W3C issues separate guidelines addressing this topic, the Authoring tool accessibility guidelines.
Open source CMS, again, are very advanced in terms of "accessible for editors with disabilities". The odd CMS even here in the Garden may still have "work in progress" to meet this requirement.
Read more: "Blind people are not our target group"