Actually there is a working port of Mosaic (well, working is an over-estimation, it renders nothing correctly) and even a fork (Mosaic-ck). The problem is, it is of limited use nowadays (much less than Trinity's Konqueror as a browser). Besides, its interface is quite ugly.
Partly Mosaic and Netscape were responsible for the mess that the Web has become, but then again they were quite innovative in their time. But using them in present-day would be frankly pointless.
-- Mavridis Philippe