I googled it and found some un-free solutions, Twitter to Identi.ca Gateway and Identi.ca to Twitter Bridge.
It seems answers were all led to twitterfeed.com.
I, personally, prefer not to sign up to so many sites, with or without OpenID.
So my question is: is there an open source project to build the bridge from Twitter to identi.ca so I can upload it to Google App Engine? A one way bridge would be nice enough. I mean, when I post on Twitter, tweets are automatically synchronized to identi.ca.