Recs.
Updated
Future proof personal knowledge app that works with Markdown files on your local disk.
SpecsUpdate
Pros

Pro Very easy to use and link notes, preserves the standard form of markdown
Linking notes is a game changing feature. Very easy to use and link notes. Their implementation of markdown doesn't deviate from the standard form of markdown and so the same files can be used by other markdown programs without any consequence.
While renaming note link still works.
Pro Multiple Vaults
A Vault in Obsidian is like a database. Internal links and files are not shared across Vaults. Each Vault is opened with a separate instance of Obsidian. Each Vault can have its unique app settings and plug-ins. Useful if you have distinct/unrelated projects or "data spaces" requiring different workflows and data relations.
Pro Infinite panes, split panes, lock panes
In Obsidian, pane = window = note = page
Obsidian allows you to open as many notes as you can fit concurrently in your screen. You can split a pane horizontally/vertically. You can lock/link panes so they scroll in sync, useful for and edit & preview modes.
Pro Helps visualize personal knowledge in ways nothing else allows
The Graph view is more than an aesthetic gizmo. It allows you to grasp and recognise clusters of information, follow branches and easily filter out what you don't want to see. The "animate" option shows how your notes and links have grown organically. With a bit of tweaking to the visuals and the proper theme, your graph might even start to look like a disturbingly "alive", eerie thing.
Pro Multiple cursors
A feature unseen in other tools.
From the help doc, "This can be useful when modifying a lot of lines in the same way, for example putting - at the beginning of multiple lines to turn them into a list, or appending [[ to a series of links you’ve copied from elsewhere."
Pro Can copy search results and paste as lists and/or links in a new or existing note
Pro Not locked to a provider
No lock-in to a certain company - just markdown files on disk.
Pro Incredible tool for PKM (Personal Knowledge Management) which allows anyone who has a computer and an internet connection to think better and create new insights
Pro Helps with planning and organization.
Variety of planning and organization plugins, such as Kanban boards or Day Planner.
Pro Supports importing from other tools
Supports importing from tools such as Notion, Evernote, OneNote, Apple Notes, Bear, Zkn3, TiddlyWiki 5, and Roam Research. Refer to Obsidian Help for more info.
Pro Discord rich presence
Update your Discord status to show your friends what are you working on with Discord Rich Presence plugin.
Cons
Con Proprietary software lock-in
Creates dependence on the application with the promise that the content is yours but that cannot be entirely true without the application being free and open source software. You will end up altering the way you create the content to take advantage of Obsidian features and your processes will evolve for its workflows. This replicates the lock-in pain that people experience moving their highly personal information from one proprietary platform to the next when that initial platform stops serving them well, goes out of business, or becomes a bad actor.
Con Requires .md files
Can't read .txt or other plaintext file formats. Can't read asciidoc files.
(Available with a plugin.)
Con Pretty new software
At this moment there is a limited amount of resources / howto's available.
Con No ability to add dates that link to a daily note, when that day/note may not yet exist
You can create a backlink which doesn't yet exist; it just doesn't auto-fill for you. (Available as a plugin)
Recommendations
Comments
Flagged Pros + Cons
Out of Date Pros + Cons
Con No mobile app <-- actually it does now!
Though it is right now in the development and you can basically use any other markdown editing apps till then.
Con No flatpak installation on Linux. Appimage or Snap only
Now supporting Flatpak: https://flathub.org/apps/details/md.obsidian.Obsidian
