Available only in, and all over  Goa, this "country liquor" is made from either coconut or the cashew apple, Going with the intent of this page, I recommend the cashew variant. 
Feni, much like other Goans, is pretty rough straight up, however, when mixed with Limca (lemon flavoured cola) transforms into a sweet, smooth and if I may say, very friendly drink (depending on the ratio of Feni to Limca), kinda like a Jack Daniels and Coke.
Again like many a Goan, it loves talking, telling every one around you of your recent (24 hours at times) association.  
Big Boss and Cashewlana are among the more famous brands available, and you'd be better off getting one of them, rather than the "best home made " Feni in Goa, which practically every Goan claims to know off (through his brother-in-law/uncle/neighbour) It's pretty clear that Feni is definitely not made at home, and that a Goan wouldn't leave is house if it really were.
However, if you still feel the need to sample some of the best home made feni, I know  of a place. (my cousin's neighbour). 

Economically priced local Goan cuisine. The crumb fried mussels, prawn curry and recheado fried Chonak (Perch) are some of the best you'll get in Goa. The lunch thali is quite sumptuous and is enjoyed by locals and tourists alike. 

Click here for directions to Anand.