Can I generate NeoGas just by holding Neo in the wallet? Does the Computer needs to be switched on all the time to generate gas?
Will there be an App for iOS and a Desktop client for Mac?
1. Yes, you just hold NEO in your wallet. The computer doesn't need to be on, and the wallet doesn't need to be running. Before you can use the Gas you generate, you will have to claim it; the exact process for doing so depends on which wallet you are using. You can claim your Gas at any time.
2. There is already a Mac wallet via CoZ (
https://github.com/CityOfZion/neon-wallet/releases/download/0.0.3c/Mac.Neon-0.0.3.dmg), and of course there are also web wallet options. I am not sure about iOS; someone else will have to help you there.