I have not heard of any software either, and I agree with everyone, wait to see what your clients use or at the very least wait till you sign a client, and if they want you to use your own software then you can purchase something.
A few years back I was part of new billing company, the founder was set on getting a software as soon as the business was registered, she wouldn't listen to anyone on waiting, that ended up costing us over $1000 before she finally listens and cancel till we get the first client.
I say, shop around, request demos and keep a list of what you like till you get that first client and decide.