OpenVPN project has a large number of active developers and contributors, who are all listed in recent changelogs (2.2-beta1, 2.1.4 and later). These changelogs are available on the ​downloads page and in the OpenVPN release packages.

To get up-to-date information you can use some Git magic. First checkout the OpenVPN development tree as described here. Then use a command like this:

$  git shortlog -e --no-merges v2.2-beta1 v2.2-beta5|grep ^Author | sort | uniq

The -e switch shows the email address of each contributor. To get a list of all tags (=frozen development tree states) use

$ git tag -l