ERPNext is an web based, open source application that helps small and medium sized business manage their Accounting, Inventory, Sales, Purchase, Manufacturing, Projects, Customer Support and Website.
Gmail is a free, advertising-supported email service offered as part of Google's G Suite, with 15GB of storage, color-coded inbox filters and unsend button.
Hypertext Markup Language (HTML) is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaScript.
PHP: Hypertext Preprocessor is a server-side scripting language designed for Web development, but also used as a general-purpose programming language. PHP code may be embedded into HTML code, or it can be used in combination with various web template systems, web content management systems, and web frameworks.