Hi! You may want to check out my app Timing for Mac. It's not free, but if you are making money as a freelancer it should be well worth it.

It's different from other time trackers in that it automatically tracks all the time you spend in different apps. You can then later assign that time to your projects and even extend the data. Makes your time tracking way more accurate than any manual time tracker! And of course you can export the data for invoicing :-)

I recently collaborated with my designer on a few mocks, and Dropbox worked well for that. I particularly liked that you could place comments at a specific location inside an image, to highlight specific UI elements.

In Google Drive you can't comment on images at all I think, which is a pretty big deal I think.

So for sharing mocks with clients, Dropbox wins hands-down.