The primary tool is a good, reliable connection to the internet. Beware some ISPs will block certain connections (ports) because of spam and other nefarious activities. Therefore do not assume that all applications will work from home. If critical the internet connection may need to be upgraded from domestic to business grade.
If all your files and applications are on the PC/Mac in the office then a remote access solution will give you access to everything as if you were in the office. For secure remote access to your PC at work you can use either Splashtop or Teamviewer. Both are free for personal use however if used for business purposes the product should be licenced. If there are sufficient number of staff working from home then enterprise licensing by the employer is the most cost effective, otherwise individual licensing should be purchased.
For remote collaboration there are a number of video and information sharing options. One of the leading applications today is Slack offering almost instantaneous team chat saving the email system from a plethora of CCs and BCCs. Other alternatives are Zoom and Skype for Business. Recently Microsoft has added Teams (Slack like application) to their Office 365 Premium offering.
An application like Trello is great for information sharing, task management and simple project management across the whole team. More sophisticated alternatives are Basecamp and Asana.
Another useful utility is a time tracking application that allows you to easily account for your time. Timely, Toggl and Everhour are the ones to check out. Need to look at your needs and then match them with the functionality of your preferred time tracking and reporting utility.