iOS: Your iDevice's built-in Contacts app leaves a little to be desired. While it can get the job done, it doesn't offer any creative features to help you organise, edit and delete your contacts easily. Tacts is a free app that does.
Tacts simply pulls from the contacts already on your device and provides you with many ways to view and edit them. You can organise by groups just like you would in the standard Contacts app, but Tacts also organises them by metadata groups. For example, you can look up people by company, location (either city or state) and a lot more. You can also organise by call frequency, view call history and discover who your favourites actually are. Bulk edits and group selects are also very easy, as you can just check off the people you want and perform the action you want to take. Overall, it's really handy if the standard Contacts app isn't quite cutting it for you.
Tacts also features a neon style, which is nice but not necessarily everyone's cup of tea. If you want to alter its appearance, however, you can through in-app purchases. You can also buy a keypad for easily adding new numbers or even searching for them. At $1.99 it seems like a lot for just a keypad, but if you like Tacts it's a way to support the developers.