There are a range of event styles that all these community groups run, so here is a breakdown of the most common event styles used
Smaller / evening events
Many communities run events for a few hours on an evening and they may include they following session styles.
The concept of lightning talks is to present a number of short presentation by different people at a snappy pace. The talks can last from 1 to 10 minutes, although its common to have 5 minute talks.
The timings can be managed strictly with someone shouting out when time is up and the presenter having to immediately stop. It is useful to have a count down or some indication of time remaining for the presenter.
To keep the pace of the lightning talks when presenters swap over, either no slides are used or all slides are loaded onto a single computer in advance.
Lightning talks are a great way to cover a number of different topics, or introduce ideas that may be at a tangent to usual topics. As talks are short in nature, this format is great for those new to presenting to try out
It is common to include lightning talks in other events such as open spaces and unconferences, or as a warm up to a longer talk.
Similar to the lightening talk but lasting longer (as thunder lasts longer than lightning in nature). Thunder talks often last for up to 20 minutes. Thunder talks are often mixed in with Lightning talks.
Pecha Kucha Night
A Pecha Kucha Night events consist of around a dozen presentations, each presenter having 20 slides, each shown for 20 seconds. Each presenter has just 6 minutes 40 seconds to explain their ideas before the next presenter takes the stage.
Pecha Kucha night is very popular with artists and other creative people for showcasing their works.
Ignite is similar to Pecha Kucha, this time participants are given 5 minutes to speak on a subject accompanied by 20 slides. Each slide is displayed for 15 seconds, and slides are automatically advanced.
Borrowing the concept of speed dating, speed geeking allows several small groups to get intimate talks.
Presenters are spread around the edged of the room and the audience is split into small groups, one group per presenter. When signalled, each presenter talks to their group for 5 minutes, answering any questions along the way. Each subsequent bell the groups move to the next presenter until the groups have seen each presenter.
The biggest problem with this style of event is presenter tedium. If there are 10 presenters at the event, the presenters have to give their talk 10 times. However, this kind of event is good for those presenters who want to improve there presentational skills with deliberate practice.
Longer / all day / several day events
There are many events that run all day or for several days, usually over a weekend. These events may include lightning and thunder talks, etc.
An unconference is a facilitated event in which the sessions (talks, workshops) are created and given by those in attendance, rather than an organised list of public speakers.
Facilitation provides a basic structure for the day, for example how many sessions are going to be held during the event and how long those sessions should be.
Attendees take one or more cards and write down the sessions they want to run, placing them on the schedule board created previously by the event facilitators.
An open space event is quite similar to an Unconference, although typically even less facilitated. The event is facilitated
A hack day is an event where developers, designers and people with ideas gather to develop one or more projects. A hack day may include some up front talks around a topic of the hack day, or presentation of one or more ideas that will be developed during the event.
At the end of the hack day (or days) it is common to have presentations of the hacks to the audience of peers and even awarding prizes.
Open conference organizers seek to open access to the conference for attendees by elimination of cost (relying on community support and sponsorships), they also provide community access to archived presentations and discussions through similar licensing agreements.
Additionally, attendees are encouraged to become participants in a collaborative community that supports and grows the conference--even to derive new open conferences.
Foo Camp and Bar Camp are other examples similar to the unconference, open space, open conference event styles.
I am currently an organiser for several communities, including the London Java Community, Graduate Development Community, London Scala user group, Limited WIP Society and Ubuntu-UK. I have organised open conference events and facilitated open spaces and found them a great way to share knowledge throughout a community.