If you're using Nameless version 1, you can find addons
here, and without adding your own PHP pages manually (in theĀ
pagesĀ folder, using
this as a template), the only way to add custom HTML pages is through the custom pages tab in the AdminCP, using the editor, although the HTML you have available is limited.
If you're using the version 2 pre-releases, you can find modules
here, and you can add any custom HTML in the custom page editor's "Source" tab through the AdminCP.
Hope that helps.