Mackall first announced Mercurial on April 19, 2005.The impetus for this was the announcement earlier that month by Bitmover that they were withdrawing the free version of BitKeeper.
BitKeeper had been used for the version control requirements of the Linux kernel project. Mackall decided to write a distributed version control system as a replacement for use with the Linux kernel. This project started a few days after another project called Git, started by Linus Torvalds with similar aims.
The Linux kernel project decided to use Git rather than Mercurial, but Mercurial is now used by many other projects.
Tyrael