There are several app building software options available that allow you to build apps offline without requiring an internet connection. However, the “best” option for you depends on your specific needs and preferences.

Here are a few options to consider:

1. Android Studio: Android Studio is the official integrated development environment (IDE) for Android app development. It is free, powerful, and can be used offline to create complex Android apps.
2. Xcode: Xcode is the official IDE for iOS app development and can be used offline to develop iOS apps. It is only available for macOS, however.
3. Visual Studio: Visual Studio is a powerful IDE that can be used for building apps across multiple platforms, including Android, iOS, and Windows. It supports offline development and offers a range of features for building robust apps.
4. Appcelerator: Appcelerator is a cross-platform app development platform that allows you to build native apps for iOS and Android using a single codebase. It can be used offline and offers a range of tools and features for building apps.
5. PhoneGap: PhoneGap is an open-source framework that allows you to build cross-platform mobile apps using HTML, CSS, and JavaScript. It can be used offline and is a popular choice for developers who want to build hybrid mobile apps.

These are just a few of the many options available for offline app building software. It’s important to consider your specific needs and goals when selecting a platform, as each has its own strengths and weaknesses.