I would like to have different applications under the same domain using Heroku.
Because of the name of the domain, I would like to access the applications using folders (mydomain.com/app) instead of using subdomains (app.mydomain.com), is this possible? Thanks
There is no type of URL re-writing you have access over thats going to do that for you. You could create a "stub" Siantra-based app that allows you to define those types of URLs, but it would have to effectively redirect you to the subdomain version.
I'd have to play devil's advocate and ask why you'd want to have things namespaced as /app instead of using subdomains. Subdomains offer much more flexibility and are a lot less brittle than essentially having to url-rewrite all the time based on the first "slash" element.