Roam Research has more features than are obvious at first glance; few products have everything that Roam has in one place. For instance, it can turn an outline into a Kanban board, which is rather unique.
The core features to Roam Research are:
[[double brackets]]around any word or phrase to create a link to that page or make a new page if that doesn't exist in your database yet.
Many outline tools—including Workflowy and OmniOutliner—have similar tools to list outlines, move points around, and zoom in to focus on one section.
A growing number of tools have wiki style links. Bear Notes is a popular notes app with wiki style links, and the Drafts notes app recently added wiki link support. I expect we'll see this style of internal linking coming to more apps over time. And, of course, wiki apps such as TiddlyWiki or even MediaWiki (the wiki behind Wikipedia) support wiki style links. Nuclino is a newer wiki option here.
Bidirectional links are far more rare. You will find them in MediaWiki; every Wikipedia page includes a "What links here" section to see pages referenced that page. So you could run that on a private server to get your own version of something similar. Obsidian is a new beta notes app that has bidirectional links, too.
Graph view is something you'll mostly see in mindmapping apps—many of which can import an outline file to turn it into a map—but not as often built into writing apps. Obsidian also has a graph view. There's a TiddlyWiki add-on to add a graph view. Observable is a developer focused notes app that is built around building unique visualizations, with more than just graphs.
Then on embedding note sections, RemNote is a study tool an interesting twist on the idea, where you can reference other sections and see their definitions in a preview.
For an app that puts everything together, Notion is often compared to Roam Research, but as noted in this Roam Research vs Notion debate, they're quite different. Both include a ton of features packed into what at first glance looks like a simple notes app; both let you format text in Markdown, and have ways to embed content. That's pretty much where the similarities end. Roam's simpler, with almost no interface, built around plain text and markdown and links, and on showing connections between ideas. Notion's built around more graphical features, with built-in databases and embeds from 3rd party apps and nested notes, rich text formatting by default, and where you link to other notes and organize them in hierarchies but don't randomly link words wiki-style. You can accomplish similar goals in both apps, but you'll come at them differently.
When it comes to outline tools I suggest moo.do.
Moo.do combines both trello and workflowy. You can substitute bi-directional links with hashtags. But I don't think you can do embedding sections in this app.
On the plus side it has cross-platform support across ios, mac, android, and web.
I'm co-founder of CogSci Apps Corp. Our Hook productivity app is not an alternative to Roam. However, Hook works well with Roam. Hook supplies the missing [bidirectional] links to macOS itself.
Hook's nimble UI looks/behaves a bit like a launcher (LaunchBar, Alfred, QuickSilver). You invoke it, issue a command, and it goes away.
Hook's main command is
Copy Link, which you can use on any file, web resource, and most objects (Mail messages, OmniFocus tasks, etc.). You can paste a link anywhere of course. So you could bidirectionally connect a Roam note to a PDF, folder, file in Git, etc.
We call Hook bidirectional links "hooks". They show up in the launcher-like Hook window when invoked in the context of the linked resource.
There are other other commands to rapidly link and access related information (e.g., ⌘N
Hook to New , ⌘M
Copy Markdown Link and ⌘R
Reveal File in Finder, ⇧⌘
Make Hook File).
Launchers are for context free access; Hook is for context-sensitive navigation. They too work well together. (Hook even has a LaunchBar action and Alfred workflow).
We designed Hook for researchers, developers, note-takers, writers, software enthusiasts, and and others who value their time/ productivity.
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