These websites have all the stuff you’d need for a standard
Dungeons and Dragons game, you will still need to get the books and your own
dice, however these sites help to enhance the game
Hero Forge and Spell Forge are two very useful character
creation tools, the DM will determine which books will be allowed, the site
update periodically however the group will use the same version that the DM
has. However it only runs on Microsoft Excel and to run it go to Tools > Macro > Security > Setting: Low. You will then need to close all Excel files and open it again for the change to take place
The SRD has all the information for a core rule game in an
easy to access format, however you will still need the books as some rules and
monsters are Dungeons and Dragons trademarked.
If you do not have Microsoft Office than this is a useful
character creator, you will need to have Java installed on your computer in order
to run this though.