Regardless of what you are writing or editing, even beta reading, there are some useful sites on the Net to use for grammar and punctuation rules, thesaurus, dictionary and etc. I often use them when editing a book:
The free dictionary – dictionary/thesaurus, legal/financial/medical dictionary, idioms and encyclopedia
Thesaurus/dictionary/encyclopedia/translator – all in one – very useful resource with a lot of useful information
Grammar tips – it is a blog with grammar and punctuation tips for SAT or freshman but if you have forgot the grammar rules this is a good place to refresh your memory.
Meriam Webster online – America’s foremost publisher of language-related reference works. The Merriam-Webster Online Dictionary is based on the print version of Merriam-Webster’s Collegiate® Dictionary, Eleventh Edition. The online dictionary includes the main A-Z listing of the Collegiate Dictionary, as well as the Abbreviations, Foreign Words and Phrases, Biographical Names, and Geographical Names sections of that book. It also includes 1,000 illustrations and 25 tables (the information is taken directly from Meriam Webster FAQ page).
Synonym – Synonym.com is the web’s best resource for English synonyms, antonyms, and definitions.
Synonym.net – is another web resource for synonyms and antonyms
Google dictionary – over 15 languages to choose from. The result gives you the meaning and pronounciation of the word, the corresponding translation in other languages, usage examples and list of web definitions.
Google translate – if you need to use a foreign language in your creative work and you are unfamiliar with the language, you could use google translate for help. Note that the translation most of the time is disastorous, but helps with simple sentences.
Law dictionary – if you need to find the correct definition of a legal term, this is your place
Legal Dictionary -from A to Z legal terms explained
Meical dictionary – A-Z list of medical terms. On the site you could also find picture slideshows, diseases and conditions, symptoms and signs, procedures and test and of course medication. Very resourceful and helpful
Acronym finder – if you search for an acronym this is a good place to start
Abbreviations – comprehensive directory and search engine for acronyms, abbreviations and initialisms on the Internet.