InfoPath is not required. You have different options with the Browser interface, SharePoint Designer, and Visual Studio.
You do however need InfoPath installed to make use of the "Customize Form" button in the ribbon - as this is expected to open in InfoPath.
Create a test list and then open the list in SharePoint Designer. You will see the forms listed (Display, Edit, New) and you can open all of these in Edit mode and make changes. You can also copy or create new pages here and then associate them with the appropriate list action.
The third option is Visual Studio - this is the hammer, and generally you are probably going to be deploying a solution which includes your column and list definitions, list instance, and custom forms all packaged up as a solution or app.