A personal wiki is a private Wikipedia with one contributor. One page per thing, pages link to each other by name, and there is no folder tree at all.
That last part is the whole idea, and it is the reason a wiki feels different from a folder of documents even when the underlying files are identical.
What makes it a wiki
Ward Cunningham built the first one in 1995 on a simple bet: if creating a link is easier than deciding where a page belongs, people will link, and the links will produce a better structure than any hierarchy they would have designed.
Three properties follow from that, and all three are what you are actually adopting.
Pages are named, and the name is the address. You do not navigate to a page, you refer to it. Writing [[compound interest]] in the middle of a sentence creates the reference, and typically creates the page too if it does not exist yet. Naming therefore does most of the organisational work, which is why how to name notes matters far more here than in a folder system.
Links are cheap and bidirectional. Any page can link to any other with no thought about where either one sits. Good wiki software shows you the reverse view, so a page knows what refers to it. See backlinks.
There is no canonical location. A page about a person can be reached from the project they worked on, the book they wrote, and the conversation you had. In a folder tree you would have had to pick one and pretend the others do not exist.
What a personal wiki is genuinely good at
Things that persist and get refined. A wiki page is a living document, not a dated entry. Your page on a programming language, a medical condition, a city you visit often, or a person you work with should get better every time you touch it. This is the evergreen notes idea with a different name and an older pedigree.
Reference knowledge you return to. How your home network is configured. The command you can never remember. Your recurring travel checklist. This material has no natural folder and enormous value, and it is where a personal wiki most obviously beats both a document folder and a chat search.
Domains with many cross-cutting entities. Anything where the same names keep recurring in different contexts: research areas, a game world, a family history, a codebase. The web of references is the actual shape of the knowledge, and a wiki is the only structure that can represent it honestly. See knowledge graph.
Where it fails
Anything with a timestamp. Meeting notes, journal entries and daily logs are events, not topics. They do not improve with editing, they should not be merged, and a wiki full of them stops being an encyclopedia and becomes a badly indexed diary. Keep those separate: see daily notes and how to take meeting notes.
Project material with deadlines. A wiki has no concept of done. Commitments need a system that does, which is what the PARA method is for.
The blank encyclopedia problem. Wikipedia is useful because it is finished. Your wiki, in month two, is forty stubs and three real pages, and it will feel like a failure by comparison. Most abandoned personal wikis die here, of unfavourable comparison to a thing built by hundreds of thousands of people.
Link rot by renaming. Rename a page and every reference to it either breaks or has to be rewritten. Good tools handle this automatically. Verify yours does before you have four hundred pages.
Building one that survives
Start from what you look up, not from what you know. The temptation is to sit down and write the pages you think should exist. Do the opposite: for two weeks, every time you look something up for the second time, make a page. The wiki grows along the lines of your actual repeated need, and every page is load-bearing from the day it exists.
Let stubs exist. A page with one line is fine, and a red link to a page you have not written is better than no reference. Wikis are supposed to have holes; the holes are a to-do list.
Write titles as things, not sentences. Espresso grind settings, not Notes on how I finally fixed the grind. The title is what you will type when you link to it in eight months, so it needs to be the obvious name for the thing.
Add one index page. A single hand-maintained front door listing the main entry points. This is the one page allowed to be a list of links, and it is what makes a wiki navigable before it is big enough to navigate itself. See maps of content.
Refactor occasionally. The genuinely wiki-specific habit: when a page gets long and covers two things, split it and link the halves. When two pages say the same thing, merge them. Doing this quarterly is the difference between a wiki and a pile. See how to declutter your notes.
What to build it in
Almost anything with wiki-style links will do, and the choice matters much less than the habit.
- Obsidian, Logseq, or any Markdown app with
[[links]]is the common modern answer, and it gives you plain text notes you can still read in twenty years. - TiddlyWiki is the eccentric classic: the entire wiki is one HTML file that you can email to yourself. Genuinely durable, genuinely idiosyncratic, still actively developed after two decades.
- A real wiki engine such as MediaWiki or DokuWiki if you want page history and are comfortable running a server. Overkill for one person, unbeatable for revision history.
- Apple Notes, Notion, or whatever you already use if it supports linking between notes. A wiki is a convention, not a product, and switching tools to get one is usually procrastination. See PKM mistakes.
The only requirement worth being firm about is that links must be easy to make while writing. If creating a reference takes more than a couple of keystrokes, you will not do it, and without links you have a folder with extra steps.
Wiki or slip-box
They look similar and they are not. A Zettelkasten is a network of individual ideas, written once and connected to argue with each other. A wiki is a set of topics, rewritten repeatedly until each is accurate.
If you want a machine for producing new thoughts, build a slip-box. If you want a reliable personal reference for the things you keep needing, build a wiki. Plenty of people run both, and the difference is simply whether a page is meant to be finished.
More in personal knowledge management, linking your thinking, and what is a digital garden.