I developed an Android app called Keep Score that let's you keep the score at sporting events. I recently added tennis to the list of sports that you can do. If anybody wants to check it out and give me feedback, I'd appreciate it.
For right now, it is just standard scoring... 2 out of 3 sets with ad scoring and 7-point tiebreakers at 6-6.
Here is the link:
And there is also a PRO version that gets rids of ads and lets you select a few different themes.