BlitzMax vs FlatRedBall

You can compile on Windows, Mac and Linux. Nothing to change. There are solutions to compile on the same machine for 2 targets.

There are many modules to extend the features of the language: you can create PDF (via a Cairo module), or just download/upload files (via LibCurl), playing streaming sound (via BASS) and so on (databases, xml, xls...) User can create their own module (they could be written in plain BlitzMax)

Based on BASIC syntax. Supports OOP, collections (array, list and map)

After many years the language it self is very stable. The packages contains the source code of ALL modules (excluding the source of the compiler).

BlitzMax is just ready after the installation. Open the IDE, write your code and just press F5 to see the results. You don't need to install other things to use the language. Of course if you want to change the language itself - or modules - you need to install MinGW or other libs, but guidelines are provided and easy to follow.

With comparison to the some of the other languages Blitzmax compiles source files fast enough.

Good performance thanks to native code on each of the target platforms.

The language is garbage collected in two modes: reference counting or using the Boehm-Demers-Weiser conservative garbage collector.

BlitzMax provides the MaxGUI modules that allow to build GUI desktop applications for Windows, Mac and Linux (FLTK or GTK via a module). You also could create your own 'gadgets'.

the forum is plenty of examples and solutions! Community is strong and still working, available for getting an hand

BLIde is an integrated development environment for Blitz Max, designed to work very close to the project file management performed by BlitzMax engine.
It’s inspired by the .NET IDE and some other great tools, It’s been designed for hobbyist and professional coders.

Just check the commit frequency on github :)
https://github.com/vchelaru/FlatRedBall/commits/master

Plus Victor takes community input seriously and is known to shift around priorities based on the pressing needs of the community

Simplifies routine tasks such as adding entities and files to the game, or tuning parameters, via the FRB Editor called Glue

Very active chat on gitter: https://gitter.im/vchelaru/FlatRedBall
Victor (the creator of the engine) is available throughout the day to answer questions and solve any problems that may arise, along with the rest of the community members who are ready to assist in any way they can.

http://flatredball.com/documentation/
Very good documentation not only regarding the API details, but also lots of tutorials covering different aspects of using FRB, either on the code-side or on using any of its tools.