Evernote. The trusted app helps keep my various projects organized, whether for work or play. An awesome development that I have discovered recently are the various services connected to Evernote, many which have been incredibly helpful to me as a freelancer. Here are a few for Android and iPad that make being your own boss easier than ever.
DocuSign Ink: Is a great way to get contracts signed and because it plays nicely with Evernote you can easily keep the contracts organised along with the rest of the project data.
Expensify: The best tool I have found for keeping receipts together. Expensify makes matching receipts to clients and projects a snap and the Evernote integration just adds to the awesomeness of this app. http://trunk.evernote.com/app/expensify/web-apps
Pocket: While I don't use Pocket solely for work, it's quite helpful for collecting information, including videos, for later perusal. Pocket lets you gather up info for later offline reading/ viewing and it's an excellent complement to Evernote.
Freelancers, what are your must-have apps?
(Top Image: Joelle Alcaidinho, all others as linked above)