--export-marks=<file> 

Dumps the internal marks table to <file> when
complete. Marks are written one per line as :markid SHA-1. Frontends
can use this file to validate imports after they have been completed,
or to save the marks table across incremental runs. As <file> is only
opened and truncated at checkpoint (or completion) the same path can
also be safely given to --import-marks.

--import-marks=<file> 

Before processing any input, load the marks specified in <file>. The
input file must exist, must be readable, and must use the same format
as produced by --export-marks.

This would (hopefully) enable Fossil users to keep using Fossil while collaborating with other SCM systems, something what one can e.g. achieve with Bazaar by using bzr-{hg,git,svn} plugins.

joerg added on 2011-09-12 13:19:30 UTC:
"fossil export" supports marker files. It doesn't work reliably for git though as it tends to fail on the git side during testing. It was complaining about missing objects, which are clearly part of an earlier import.