1. most ruby code can't be used in crystal, but is trivial to port.
2. Crystal doesn't use gems (because of 1). it uses shards.
Lack of multithreading is an issue for _ME_ because i'm working on an app that could really benefit from it. Just because Ruby is used almost exclusively for webapps doesn't mean Crystal is. Also, the "load another copy of the entire app into memory" that Rails people use is a really crappy way of doing "multithreading" .