When comparing Gosu vs Buildbox, the Slant community recommends Gosu for most people. In the question“What are the best 2D game engines?” Gosu is ranked 50th while Buildbox is ranked 51st. The most important reason people chose Gosu is:
Gosu is not a game development framework, only a media library that happens to be suited to game development. (Kind of like SDL in the C world.) That means the interface is relatively small.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Lightweight
Gosu is not a game development framework, only a media library that happens to be suited to game development. (Kind of like SDL in the C world.) That means the interface is relatively small.
Pro Mature API, actively maintained and developed
Gosu has been under development since 2001. It is mature and has several toolkits built on top of it to provide additional functionality.

Pro Cross-platform, even mobile, using Ruby

Pro Drag - and - drop editor
Drag - and - drop editor without writing any line of code.
Pro Easy to learn
Buildbox is a drag and drop engine, making it easy for beginners to pick up. There are many tutorials available to help get you started.
Pro Has many game templates
Buildbox has 20+ different game templates including templates for platformers, racing games and Flappy Bird clones.
Pro Built-in support for ads
You can add banner and interstitial ads from multiple ad networks, including AdMob, RevMob, Facebook. They can work with Amazon's, Microsoft's, Google's and Apple's app stores.
Pro Develop once publish everywhere
Exporting iOS/Android/macOS/Windows/Steam/Amazon
Pro Cross-platform
Cons
Con Deploying Ruby apps is a mess
Games built with the Ruby to .exe "compiler" do nothing more than extract your source code and Ruby.exe to %TEMP%, then run it. The code is not really compiled at all. The process for wrapping games as Mac apps is a bit nicer, but you'll need a paid Apple Developer subscription to code sign the app, or users will see a warning/error when running your game.
The only way to really compile Ruby is to use RubyMotion, which does not work on Windows and requires a paid subscription on top of the Apple Developer one.
(This Con is not specific to Gosu. Deploying Ruby code has never been fun.)
Con Incredibly Expensive
$99/mo for full functionality probably makes this the least accessible piece of game development software in regards to price, all with a very limiting feature set.
Con You are restricted by it's limitations
For example, you can only make certain kind of games.
Con Not very powerful
You will be limited to using templates to build games.
Con Subscription Model
The two more reasonable price points limit the functionality of a software already far less powerful than many more cost effective alternatives.

Con Very expensive
Buildbox has a 15-day trial version, after that a $2675 license to use it must be bought.
Con Stability Issues
The software has stability issues on Windows, with the preview window causing program crashes when simple functionality is added.
