tesseract is the only real alternative that runs natively on linux. Try it for yourself and see if it works for you. It is a command line utility but there're some GUI frontends, like
GimageReader.
Since you're in Ubuntu I think you can install gImageReader from a ppa.
FineReader might be from better to waaaaay better depending on the source document and language used. But if you're using english or other wide used language based on the latin alphabet you won't loose anything for trying.