Fossil

Check-in 2 of Figure 3 is considered a "fork"
because it has two children in the same branch.  Check-in 2 of Figure 5
also has two children, but each child is in a different branch, hence in
Figure 5, check-in 2 is considered a "branch point."

<h2>Differences With Other DVCSes</h2>

<h3 id="single">Single DAG</h3>

Fossil keeps all check-ins on a single DAG.  Branches are identified with
tags.  This means that check-ins can be freely moved between branches
simply by altering their tags.

Most other DVCSes maintain a separate DAG for each branch.

<h3 id="unique">Branch Names Need Not Be Unique</h3>

Fossil does not require that branch names be unique, as in some VCSes,
most notably Git. Just as with unnamed branches (which we call forks)
Fossil resolves such ambiguities using the timestamps on the latest
checkin in each branch. If you have two branches named "foo" and you say
<b>fossil up foo</b>, you get the tip of the "foo" branch with the most
recent checkin.

This fact is helpful because it means you can reuse branch names, which
is especially useful with utility branches.  There are several of these
in the SQLite and Fossil repositories: "broken-build," "declined,"
"mistake," etc. As you might guess from these names, such branch names
are used in renaming the tip of one branch to shunt it off away from the
mainline of that branch due to some human error. (See <b>fossil
amend</b> and the Fossil UI checkin ammendment features.) This is a
workaround for Fossil's [./shunning.wiki|normal inability to forget
history]: we usually don't want to actually <i>remove</i> history, but
would like to sometimes set some of it aside under a new label.

Because some VCSes can't cope with duplicate branch names, Fossil
collapses such names down on export using the same timestamp based
arbitration logic, so that only the branch with the newest checkin gets
the branch name in the export.

All of the above is true of tags in general, not just branches.