When comparing Gosu vs BYOND, the Slant community recommends BYOND for most people. In the question“What are the best 2D game engines?” BYOND is ranked 29th while Gosu is ranked 50th. The most important reason people chose BYOND is:
BYOND is in active development and updates are released constantly.
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 In active development
BYOND is in active development and updates are released constantly.
Pro Easy to use
The software itself is very easy to learn and use for beginners.
Pro Helpful community
BYOND's community is relatively large and extremely helpful. Any question a beginner or an experienced user may have is quickly answered.
Pro Large Community
Fairly large player base and multiple games to play.
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 Highly supports multiplayer, but can make solo games ready for download.
Con Exclusive programming language
The language is known as DM, and is modified using Dream Maker. It is an object oriented, interpreted language, which closely resembles C++, Java and PHP. More information available in the DM Guide.
