Two productivity apps we use all the time are toggl and CloudApp. Both apps are free and do different things that are helpful if you have clients.
Toggle is a time tracking app that allows you to name what you are working on. The time is adjustable if you forget to turn it on.
The nice feature about toggle is that it is cloud based and you can set it up on more than one computer and it stays in sync. Toggle will also send you a weekly report so you know how much time you spent working on company x. Toggl has more advanced features like tracking for teams, but these are features that are paid for.
CloudApp is a photo editing app. The app is cloud based and your image receives it’s own link so you can email it. The way it works is first you take a screenshot, then you drop the screenshot onto the icon and it instantly gives you a link to the image.
At the same time the image editor pops up. This is very handy for adding notations such as arrows or circles to your image. This is useful if you are trying to give someone a set of instructions.
Both productivity apps work great in the free mode, but they do have more benefits if you want to upgrade and pay for them.