Ruby <i>might</i> just need a better implementation with more time spent on optimization.  <a href="http://maglev.gemstone.com/" rel="nofollow">http://maglev.gemstone.com/</a> is going in this direction.<p>But also, Lua was always designed with cleanness and simplicity of implementation in mind.  Its developers have strong backgrounds in both theory and engineering, which you can see in their interview in the book <i>Masterminds of Programming</i>.  They've been very conservative about the design of the language.  In contrast, Ruby feels much messier and more "evolved" - look at its Yacc grammar[1], for example, compared to the grammar of JavaScript or Lua[2].  Even the Ruby lexer is full of weird edge cases.  Much of MRI is like that, and for years it was the only "spec" for the language; now its decisions have been reverse-engineered and inherited by all other implementations.<p>[1]: <a href="http://blog.nicksieger.com/articles/2006/10/27/visualization-of-rubys-grammar" rel="nofollow">http://blog.nicksieger.com/articles/2006/10/27/visualization...</a><p>[2]: <a href="http://www.lua.org/manual/5.1/manual.html#8" rel="nofollow">http://www.lua.org/manual/5.1/manual.html#8</a><p>[By the way, I've used Ruby for years and like it at lot, while I've written only a few lines of Lua code and like it but am not deeply familiar with it.]