Supernote is decent in this regard. It's an android base, but the software has been very intentionally designed so as to avoid many of the pitfalls. It's primarily a notetaking e-ink tablet, it excels at writing notes or marking up pdfs/ebooks. If you really want you are able to install other applications, currently not officially supported though they've said they plan on adding support, but it's completely secondary to the primary mostly seamless design.