Google Voice is a VoIP software that allows users to make and take calls from any device with an internet connection. Fees cost $0–$30/user/month.
Google Hangouts provides users with various communications channels such as text, voice or video chats. It is free to use.
Boomerang for Gmail is designed to boost email productivity for Gmail and Google Apps users. Prices range from $0-$49.99/month.
Facebook Pages Manager is a free app that enables users to connect and manage up to 50 Pages—all in one place.
PayPal Business is an online invoicing & payment processing services provider. Rates start at 2.9% + $0.30/transaction.