I know that web.py was around years before Sinatra. But URL routing in Bottle is more similar to Sinatra than it is to the URL dispatching via a tuple at the top of a file. Even so, perhaps Bottle is influenced more by web.py. That doesn't mean there aren't a ton of ports of Sinatra (like Express for node.js, Scalatra) or those influence by Sinatra like itty (http://toastdriven.com/blog/2009/mar/07/itty-sinatra-inspire...) or even perhaps Flask.
I even noticed a comment above that said Bottle looks just like Itty. Yet because I brought up the Ruby framework that Itty is essentially a port of, I'm getting down-voted like crazy. I will never understand why Python people dislike Ruby so much, and vice versa.