Calendar

Sunbird

Mozilla's Thunderbird (our e-mail pick; see that category below) lacks a calendar, so most business users rely on the equally free Sunbird for scheduling. It's a very straightforward application, with day, week, and month views, and even a publishing feature to enable sending your calendar to a Web site, should you wish to make it public. Get the Lightning plug-in to integrate Sunbird directly with Thunderbird. (free)

Collaboration

Vyew

With Vyew, anyone can host an Internet session that lets scattered colleagues work together on a project in real time. This Web conferencing platform gives you a very simple whiteboard where you can upload documents for discussion, share your desktop, or create designs from scratch. You don't even have to register to use Vyew, but if you do, you get access to VoIP and other audio services. (free for up to 20 live participants; additional services extra)

Collaboration/Office Suite

Google Docs

If your team members all have Google accounts (and why wouldn't they?), sharing files and collaborating on them simultaneously and in real-time is a snap with Google Docs. A word processor and spreadsheet are your only choices--no free-form whiteboarding here--but the service is free and easy as pie to operate. Upgrading to the Premier Edition brings extra space (a 25GB limit versus 7GB for free) and a conference-room scheduling system. (Standard Edition is free)

CRM

Salesforce.com

Customer relationship management isn't just for the Fortune 500. Even one-person shops can benefit from a more ordered approach to managing the sales process, tracking leads, and ensuring that follow-ups are done in a timely fashion. Salesforce.com requires some training and patience due to its vastness, but its exhaustive feature set and affordable pricing options make it a business must-have. ($8.25 to $250 per user per month)

Database

FileMaker Pro

Access is a part of many editions of Microsoft Office, but if you don't already have that database program in your toolkit, consider springing for FileMaker Pro instead. This database application is more intuitive than Access, while offering high-end features like live SQL data source support and easy Web-publishing capabilities, so your whole team can access the database via a browser. And its array of prebuilt templates helps you get up and running in no time. ($299)