Some Vrat or fasts are kept on special Tithi only such as Poornimaa, Ekaadashee etc. Here are the fasts listed according to Tithi --

Pratipadaa Vrat (1st Day)
Dwiteeya (2nd Day)
Triteeyaa Vrat(3rd Day) - see  Bhavishya Puraan, 1/8
Chaturthee Vrat (4th Day) -
--Ganesh Chaturthee,
--Sankathaara Chaturthee
--Shaantaa Chaturthee,
--Shivaa Chaturthee,
--Sukha Chaturthee

Panchamee Vrat (5th Day)
Shashthee Vrat (6th Day)
Saptamee Vrat (7th Day)
Ashtamee Vrat (8th Day)
Navamee Vrat (9th Day)
Dashamee Vrat (10th Day)
Ekaadashee Vrat (11th Day)
Dwaadashee Vrat (12th Day)
Trayodashee Vrat(13th Day)
--Pradosh Vrat
--Kaam Dev

Chaturdashee Vrat (14th Day)
Amaavasyaa Vrat (15th Day)
Poornimaa Vrat (15th Day)
Bheeshm Panchak Vrat