Parallel pages have been central to the Xanadu project since 1970. I am continuing to work on that with the great Edward Betts, in England. (As to the classic Xanadu system, Roger Gregory hopes to get it working on a single server, without the federation module.) MEANWHILE, I want to acknowledge parallel document work by others-- = MISSED WHEN THIS WAS SHOT: I didn't know about Norm Meyrowitz' "Intermedia" system, at Brown University-- it had bidirectional links, but alas locked to a long-lost Macintosh version of Unix (never trust Apple to let you keep using something!) https://en.wikipedia.org/wiki/Intermedia_(hypertext) I didn't see it until the Engelbart 50th anniversary fest on 9 December 2018, when Norm somehow got it running for the occasion. = Dame Wendy Hall's Microcosm (no longer active), which she's told me was inspired by Xanadu-- they got two-way links by putting the links in a database. It's a good method (but it didn't show parallel pages). = Adam C. Moore's parallel document site-- his DOCUPLEXTRON, a "document environment for reading, writing, and working with hypertexts". (inactive as of December 2018-- but there's a video) at alpha.io. This is interactively close to the Xanadu design, though technically very different. = PARALLEL DOCUMENTS ON PAPER: There have been a number of software systems that allow parallelism in paper layouts, but not interactive pages. These include PageMaker, Quark Express and InDesign. Paper paralleiism is wonderfully shown in Alden Bevington's book with side-notes commenting on every page-- OPEN COLLABORATION, by Alpha Lo and Alden Bevington. This book was laid out using Adobe InDesign;. (And InDesign can output as PDF, but that's not interactive.) So that's a system that allows parallelism in PAPER SIMULATION, but not with interaction. There have been several other systems that allowed parallel simulations of paper, including PageMaker and Quark Express. = PUBLIC ANNOTATION SITE by Dan Whaley (nonprofit, open source)-- hypothes.is As I understand it, this permits multiple annotations on a single Web page. These cannot be shown with visible connection or editorially selected and grouped. Whaley's system is an achievement, but a different achievement from the genre of connected parallel windows that I have been talking about. = BROWSING OF CONNECTED PUBLIC DOCUMENTS by Miëtek Bak, as recommended by Michael Karpeles-- -- archived at https://web.archive.org/web/20180118042327/http://sourceoftruth.net/ This allows browsing along visible connections in a Miller Column-like interface, shown in this video. Why it's only archived and not live, I don't know. === There are probably other such endeavors-- this is clearly an important realm-- but they are not well publicized.