Hello,
You can find the differences at this link
http://www.nc-software.com/Logbook-Pro-Flight-Log-Software-for-Pilots
Here is a summary
License:
Evaluation Restrictions: There are no time limits in the evaluation of this product which is available for free download from this web site. The only limitations are the flight log area is limited to 50 flight log entries and PDA sync is disabled until both PC and PDA products are licensed.
Standard Edition: License to install on one computer for the use of one pilot logbook file.
Professional Edition: License to install on two computer's for the use of one pilot logbook file. Additional features over Standard Edition include: PC-to-PC Sync Wizard for syncing data files across two computers, and FAR 121 and FAR 135 features.
Enterprise Edition: License to install on one computer for unlimited pilot logbook files (users). Includes Professional Edition features.
License term: Logbook Pro Desktop edition is a one time purchase, not a subscription, you are entitled to all version 1.x updates free for the life of your product. We have not charged customers for an update in over 16 years!