Myna has to be one of the coolest online applications I've seen in a long time. This is a music/sound editor very very similar to Garageband. In fact, I would use this over Audacity any time. PC users can rejoice that they now can create music similar to Garageband.
All you have to do is get started is to create an account, click on the app you want to use (audio editor) and start experimenting w/ all types of music. One of the advantages that Garageband has over Mya is the ability to not only add pre-set tracks but to add individual instruments as well. You literally can create an original piece of music from scratch. Myna has actual preset audio tracks that you can mix/mash.
I highly highly recommend giving Mya a try by clicking here you won't be disappointed.
Below is my sample audio mix w/ my voice recorded over it 8-)