Resilio Sync (formerly Bit Torrent Sync) by Resilio, Inc.
This decreases the number of syscalls for reading data. Similarly, for write requests, blocks are cached and flushed to disk once one full piece is complete or the piece is the least recently updated one when more cache space is needed.
The cache dynamically allocates space between the write and read cache.
I know Git Hub seems to be doing many things right at the moment, but there often comes a point at which companies that have raised $100M in Venture Capital funding start making decisions that their users would strongly prefer them not to.
There are philosophical reasons, too: Git Hub is closed source, so we can’t make it better ourselves.
Some of its implementation details are described in the features section.