Castle Game Engine - An open-source 3D/2D game engine for ObjectPascal.
Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
Open 3D Engine - Open 3D Engine is an open-source 3D game development engine in real-time.
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
Godot Engine - Feature-packed 2D and 3D open source game engine.
eM Client - eM Client is a fully-featured email client for Windows and macOS with a clean and easy-to-use interface. eM Client also offers features for calendars, tasks, contacts, notes, and chat.