We don’t know many freedivers who logged their session.
Could be because there are not many ready made logbook available in the market for freedivers. SSI Freediving do have freedive logbook for the students can be purchased. Not sure about other agencies.
Mainly, if you freedive and you want to log your dive, you just wrote it down somewhere in your notebook or journal
But now, we’ve found a digital logbook specifically designed for freedivers.
It’s called APPNEA. ( https://app-nea-it.appspot.com )
Currently is in its beta version. It’s ease of use and easy registration via facebook account make it easier for you to start.
APPNEA is a social freediving logbook. By social, it means (for now) you can register and share using your facebook account. We’re sure that more social features will be added soon.

Features:
-Multi device logbook for freedivers
-Completely free
-Platform and data are hosted in the Google cloud
-APP-NEA is built around the concept of Dive Session and Dives. Freediver can create a dive session with global information about it and then can add one or more single dive to the session with more detailed data.
-Supports Facebook login access and Facebook sharing of freediver’s perfomrance.
-Shows 3-dimension data graph that reporting depth, time and duration.
-Freediver is able to create custom field both for dive session and dive.

Upcoming features:
-Support data export in csv format.

Other cool thing about this open software, is it’s an open software! The developer are kind enough to share the API access for other developers.
We are still playing around with this. This is another good stuff for freedivers to track your performance and record your progress
To start logging your freedive training and sessions, logon here https://app-nea-it.appspot.com/webclient/index.html