US companies are banned from "exporting" anything to several countries. This ban applies to software as well, so a lot of people from places like Cuba or Iran are unable to download popular software such as IM clients, email clients or even browsers from US companies, even if they are free.
But Google has been working on getting some exceptions to these restrictions, so it could offer its software to people in these countries.
It started with Iran where some software is now made available. Granted, Iran does plenty to block Google services on its own, but still, users in Iran can now get access to Picasa, Google Earth and Chrome, the three major pieces of software created by Google.
Now, the company is doing the same in Syria where Google Earth, Picasa and Chrome are currently available for download from official sources.