1.4

Yes, its open source. The tools we use (Perl, PostsgreSQL, Apache ++) are also open source.

Open source means that the source code of the software is available for free to everyone and you can modify the code and distribute it yourself. https://en.wikipedia.org/wiki/Open_source

Look for a place to contribute. This means not only programming, but also documentation, theme design, art work, or architectural design.

No, there is currently no REST api; however, one is planned.

Other APIs are not available, except for the Perl APIs the application uses itself.

Not out of the box. However, community member John Locke (from Freelock Inc) is doing it using a custom integration. He doesn't mind sharing his code.

Short answer: Yes

LedgerSMB can tie product sales to a tax class so that VAT can automatically be split off into the required VAT accounts on a sale, and when cancelling an invoice, automatically perform the reverse bookings.

Each product can be 'attached' to an account and the associated % will be applied automatically.

The LedgerSMB community follows the Ubuntu Code of Conduct.

Quite a few users find some of the terminology and accounting processes a little confusing at first. Some of the more popular small business accounting packages tend to hide these aspects of book-keeping from users for simplicity, so with the current user interface there is often some new ideas to grasp.

First step is the manual - the LedgerSMB manual is free and highly recommended reading.