Hi Muhammad, I used to use an app but they have since gone out of business. I have found this site useful - http://appcrawlr.com/ios-apps/best-apps-recording-interviews - but one way or another I would recommend that you have a second recorder available just in case!
i found using one note on my pc was brilliant. It let me record without intimidating participants; people are more accepting of having a pc in the space than an audio recorder. Once the recording was saved, I could transcribe there on on note and i could then analyse and save all the data in one space.
Most recording apps give mono recordings, but if you are using focus groups, I'd recommend spending a bit more and getting one that does stereo. That makes it easier to tell who is speaking.
FYI almost all these comments have been about recording because there is no software that will do adequate transcription of either individual or group interviews.
A friend and I just created a simple web application with the best transcribing tech out there and it is super simple. We currently have more than 80 languages available. We made it affordable to everyone at €0.09 / minute.