You can go here and on the left down a bit you will see a selection for Free Software, it is a great place to start. Also it would help if you let us know what type of app you may be looking for?
One I just came across and I would like to throw on the table is YouMail. It is a free service that gives you visual VM without having to pay your carrier monthly. I have been working with the free version (a little ad is shown) and it has been great. It can send you a SMS when you get a VM and then you open the app and their are your VM's for you to hear. Skip one and hear what ever one you want to go to first without having to listen to them all. Save it, email it to someone or if you want to get back at someone, load it up to FaceBook for all to hear. Another great feature is you are able to sign in via your browser and see and hear your VM right on your PC as well. Sorry for sounding like a salesman for the company.
I co-sign with @JimiMack.. Youmail is one great app...I love the fact my friends don't understand don't leave me a vm just to say call me and I can delete it once I see their name without listening to the message.
