Free UK Genealogy is the parent organization for FreeBMD, FreeReg and FreeCEN. Volunteers make transcriptions of the England and Wales Index of Births, Marriages and Deaths (FreeBMD), historic Parish Registers (FreeReg) and 19th Century Censuses (FreeCEN).
Each of the projects is a significant undertaking and in total, more than ten thousand volunteers have contributed over 350,000,000 records.
The three databases - FreeBMD, FreeReg, and FreeCen are completely free to access online.
If you are searching your UK ancestors, you might want to give these sites a try.