I would just save the email that the invite was sent to and save the invite against it. When the user signs up with that email I would know they have an invite waiting for them. There's a chance they might not use the same email address to sign up but this makes a much cleaner flow for the user.
This is what's wrong with your game:
- It's on Android. In my experience Android apps don't monetize as well as iOS.
- It's Sudoko. There are a lot of Sudoku apps out there.
- It's free. You probably need to change the pricing model.
Try soem of the suggestions given in the comments above and let us know what happens.
The letter from the patent trolls actually explains why they don't do that (the real reason is probably because it's easier to get a 30 person small business to pay up instead of a giant corporation with a retainer of lawyers).
I think that modern OS GUI has helped increase productivity. Not giving your kids exposure to a modern OS means that your kid would be playing catch up with other kids when exposed to one, say, in school.
A person's job prospects may also be limited if they don't know, or are not comfortable with, what the majority uses
We're talking about a five-year-old here. I think it's absurd to think that any of us know what a mainstream productivity OS is going to look like by the time it affects his "job prospects".
At that age, what matters isn't any of the material learned. It's the attitudes and self-conceptions that matter. If a five-year-old learns that he likes telling computers what to do and that he can get steadily better at it by exploring, that's a huge win for his future.
The last version of Windows I used seriously was 3.1.
Last winter, I suddenly had to fix problems in Windows Server 2008. I may have been a bit slow, but yes, I can fix an OS I've never used.
If you have a good knowledge base, and the experience to provide a good intuition, you can figure them out.
I would, incidentally, consider Debian to be a modern OS, and a CLI to be a modern UI. If they can string together commands in bash, I'm sure they'll be just fine with Windows.
* Sponsored challenges - Companies can use Deed as marketing tool for brand promotions to leverage the engagement amongst its customers/fans. In general everyone can create a challenge on Deed but businesses might pay for some extra features such as advanced analytics, fancy challenge features, support, consultation, announcement, etc.
* HR departments can use the private spaces in Deed for motivation/coaching/entertainment/assessment of their staff