When I do web development, I use a custom made logger that catches fatal errors and appends a trace to a file and displays a message to the user. I can occasionally glance
Apple automatically collects crash logs from users for you, and you can download them from iTunes connect.
If that's not enough for you, I'm not aware of a toolkit but I wouldn't want to roll something on my own, personally. It seems like too much effort to develop something robust, might raise privacy concerns, and in the end, with 100,000K apps in the app store, how many users would use your application again after discovering it was buggy?