Note to LW Admins: I was surprised this tag/explanation didn't exist, so I adapted from our Manifest X DC Attendee Guide. Recommend categorizing this wikitag under "Community".

Unlike traditional conferences with a fixed agenda, unconferences are organized by attendees on the spot. This has the advantage of attendees actively shaping the activities, discussions, and topics into the kind of event they want to have.

Here's how it generally works:

Propose Sessions: Anyone can propose a session on a topic they're passionate about or want to learn more about. Don't worry if you've never led a session before, or if your idea isn't fully formed—these are generally low-risk environments for sharing and exploring.
- Sometimes there is a scratchpad for topic ideas that are not yet scheduled, which can be helpful for polling interest in potential topics.
- Focusing on interesting digressions from discussions earlier in the day often produces many of the better sessions at these events. This is the kind of iterative, responsive content that is neglected by conferences where everything is scheduled in advance.
Schedule Sessions: Some unconferences have participants vote on proposed topics, especially if breakout space is badly constrained. Most don't, devoting at least some rooms to open first-come-first-served reservations. In larger unconferences, organizers may move or reshuffle sessions based on demand, topics, and potential conflicts, but in smaller ones this is usually not necessary.
Participate Actively: You can attend any session that interests you, move between sessions, or even start an impromptu discussion. The goal is active engagement and collaborative learning.

Some prompts for short talks:

Experiential - Some unusual but relatable experience you’ve had that others might find interesting
- Example: Someone gave a talk on their experience volunteering for political campaigns that was interesting
Skill-based - The rough outlines of how some skill works, great for encouraging participation or paired practice
- Example: Someone gave a talk on improv comedy/improv and it was really cool
How Things Work - Describe why something works the way it does. Often best if you can trace a bit of the history and describe how constraints drove particular design elements.
What X doesn’t know about Y, and what Y should know about X
- Best if it’s two people, one representing each camp, but that’s not required.

Some more involved topics that might need an hour or more:

Unfurl the Intervention Banner - At the first LessOnline, a longtime rationalist gave a talk about his world model, then scheduled an intervention. For himself. Where random attendees used his model of the world to tell him what to do with his life, or at least his next year. It was a brilliant and productive idea.
Lecture with live betting/predictions
Debate a topic that can be operationalized into a prediction market, and encourage the audience to bet as arguments sway them. Either project the market visible to all, or for bonus difficulty, project the market behind the debaters so the audience can see, but the participants can't.

Finally: Having any amount of preparation is better than not. Simply writing down an outline on an index card will dramatically improve most talks, compared to improvising everything. Don’t let this dissuade you from adding something day-of, particularly if you’re riffing off of an idea from earlier in the day. But try to take 15 minutes to sit in a quiet corner and sketch out what you want to say, how you want to structure it, and what kind of discussions you want to prompt.