A detailed explanation of what plurality is that describes several ways it can be experienced along a spectrum of dissociation. While this is primarily aimed at disordered plurality and a clinical framework, it does note the existence of other forms of plurality.
One of the earliest websites about median plurality- it actually predates the coining of the word median and uses its predecessor, midcontinuum. Contains quite a few links to anecdotal experiences of medianhood.
An explanation of median plurality with an example from the author. Fair warning that Astraea's Web itself is a horrible resource and is known for stealing the work of creators without their permission; this is practically the only page we can recommend from that site and that's only because we can't find it elsewhere.
A zine about plural selves within singlets from an Internal Family Systems perspective. It proposes that everyone has plural selves, but that they manifest more subtly for most people. Even if you disagree with the idea, it's an interesting read.
A helpful set of questions for plurals to fill out to explain how they want others to interact with them. If you're not plural, these may be some good questions to ask your plural friends if you don't know the answers.
A speculative paper on the nature of the self, theorizing that the self is the center of the story we tell about ourselves. Towards the end, it touches on plurality and notes that there's no reason one couldn't unproblematically have multiple selves.
A terminal-based notes utility made by us and designed for plural folks. It supports multiple users on a single OS user, allowing you to keep notes as individuals without ever needing to log out. In addition to creating personal notes in your preferred text editor, there's also the ability to create shared notes that everyone can view, making it easy to communicate or share information. Runs for certain on Linux; may run on MacOS and Windows but currently untested on those platforms.