Four Small Business Software Needs — And Some Open Source Solutions
There are a few choices here. The two that come immediately to mind though are LibreOffice and OpenOffice. These are also the two I'd recommend to someone who no longer sees the benefits of continuing to pay Microsoft for an office suite.
OpenOffice (download OpenOffice here) was actually the first piece of open source software I remember using. Starting at version 1, I used it right up through 3. When Oracle got hold of it after they took over Sun Microsystems, there was a bit of a fork. I migrated away with lots of other people…
LibreOffice (here's the official LibreOffice site here, but you might want to try this download method instead) was the "bit of a fork" I just mentioned. It's the office app I currently use, and what I set other people up with when I fix their computers.
With either one of these, you will be able to give your customers documents they can open, and will be able to open up pretty much whatever they throw at you.
Most open source advocated mention GIMP when the subject of graphic editing comes up. I too think of it first, but there are some other, lighter weight, apps with enough functionality to get a small business owner through some basic image editing.
Pinta falls in between something like a GIMP or Photoshop and something like the Paint app that has come with Windows for as far back as I can remember (3.1 was my first). It will perform rotations and crops, resizes, and is capable of layers if you need them.
Thunderbird — that's all I can say. Yes there are others, but this has been my main email app since it came out in 2004, and I can personally attest to how great it is. It will not, however, hook up to an exchange server. That is a deal breaker for some folks, and if they want an open source mail client for use with Outlook, I'm told they'll have to use Evolution.
Again, it's Thunderbird (mostly) that I'd recommend for this. Thunderbird has a Lightning plugin that works great with Google and CalDav type calendars. If you want to set up a calendar server of your own, good luck. I did it and wrote about it in my Open Source Calendar Software Tutorial – Radicale post that you can check out if you like, but for the squeamish or if you're in a hurry to just get up and going, set up a Google Calendar, hook Thunderbird (with the Lightning add-on) up to it, and go with that.