Dolibarr is a popular platform.

1. Dolibarr Module Development
#360
Rajib Hossain Pavel
@pavelrajib
CIO
(Courtesy::A. Korsonsky)

2. Introduction
Dolibarr is GPL Licensed Open Source PHP Project. One thing I want to tell you this
is PSR-2 Compliant though not following strict still today.
It is a Backend Management System.
It is an ERP. Or it may be more.
It has its own unique OOP Programming Model. For instance I can tell you every
object(Product, Order, Invoice etc.) inherits from CommonObject and it has Context
for User($user), Configuration($conf) and Languages($lang) available in each
module. It has Ajax Support too. A bit tricky but once you have understood the
concepts, you would praise the structure. This system may not be lightweight(there is
extensive use of XML) but it is effective.

3. Fundamental Constructs
Module Descriptor, here it is the Single File that acts like a Configuration file for a Module.
Tree of Path, here it is the Directory Structure.
Admin Management, here it allows defining some parameters from the UI.
Constants, here Parameters globally(all users) or locally(specific user).
Rights, here Admin/User Differentiator or Permissions.
Menu System.
Tab Management.
View System, here CSS and JS can be included.
Substitution Variable Management.
SQL Management, here we can have models but it can be skipped too.

4. Before Delving into Details
Do not fell into the trap of idmenu. Just make sure this value is sanitized. Do not let
anyone do XCRF Attack on your site.
Keep your Module simple. Write Code that you understand. Consult the
Documentation if you need it, I think you will need this. Check some repositories in
the Github, there are some wonderful modules and fiddle with them and you can turn
into an Expert I guess.
Attribute Licensing terms in the right manner. Do not plagiarize or steal or be unfair.
We have the basic responsibility to do honorable conduct of being fair.