Esperanto: Translation and Spellchecker software
I found this great software named Esperantilo on the web. It is good at translating from Esperanto to English(can also translate documents) and vice versa. It also has some kind of spellchecker and grammar checker integrated. In addition to these, there are thesaurus and dictionary (online) baked into the software.
Kurso is another honorable mention. It is a step by step introduction to esperanto grammar rules accompanied by occasional tests and exercises