I have used a lot of frameworks since I started iOS development. I feel that some frameworks are really great and I can't help myself, so I will share them with you. These frameworks can accelerate development, saving you from writing "bottom layer"Code.
1. asihttprequest
Many famous ASI users should have used it, such as synchronous requests, asynchronous requests, queue requests, file downloads, cookies, and cache. As long as you have encapsulated HTTP-based applications. Transport: http://allseeing-i.com/ASIHTTPRequest/
2. mbprogresshud
This is a framework for displaying the waiting status, which has a lot of effects, but it is easy to use. Its usage is in his official example. Transport: https://github.com/jdg/MBProgressHUD
3. fmdatabase
A framework that encapsulates SQLite. Transport: https://github.com/ccgus/fmdb
4. sbjson
Well, I admit this name is ugly, but no one knows about sbjson during iOS development. Transport: http://stig.github.com/json-framework/