A "Twestival" seems to be a gathering of Twitter users -- Twitter being the online social networking site that allows users to post second-by-second updates on what they're doing. ("Don Frances is getting off the train" ... "Don Frances is walking" ... "Don Frances is arriving to work" ... "Don Frances is working" ...)
There's even a Twitter site for the Mountain View Police Department (Web Link).
The truth is I don't exactly know what a Twestival is, or why the San Jose one is in Mountain View. But apparently they're happening all over the place today -- for example, here's a post about one in Washington, D.C.: Web Link. The Web site announcing the local Twestival (Web Link) offers the following explanation as to its origins:
"In September 2008, a group of Twitterers based in London UK decided to organise an event where the local Twitter community could socialize offline; meet the faces behind the avatars, enjoy some entertainment, have a few drinks and tie this in with a food drive and fundraising effort for a local homeless charity.
"The bulk of the event was organized in under two weeks, via Twitter and utilized the talents and financial support of the local Twittersphere to make this happen.
"Around the world similar stories started appearing of local Twitter communities coming together and taking action for a great cause. Twestival was born out of the idea that if cities were able to collaborate on an international scale, but working from a local level, it could have a spectacular impact."
The local Twestival is raising funds for a nonprofit called Charity: Water (Web Link). Twitterers will be gathering at Neto Caffe & Bakery (Web Link), located about 100 feet from the Voice newsroom, at 6:30 p.m.