"Colectivo" taxis in Havana are public taxis that basically act like small buses. They follow a route, well mostly, or at least sometimes.
Since 2011, they have been able to pick up foreigners.
You'll recognise them. Pre-embargo cars, not nicely fixed up, with a taxi sign in the front.
If you ever need a very cheap (cents) way of getting around Havana in something not remotely approaching comfort but in the mood to have a laugh with some locals, they're the way to go.
They have their own sign language, see video
More here
http://www.cuba-junky.com/havana/colectivo_taxi_havana.html