SynapseDirect

This poster mentions these.

OfficeAlly.com and FreeClaims.com

Not sure how good they are. 

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I've used both OfficeAlly.com and FreeClaims.com.
They allow you to submit claims electronically.
FreeClaims.com isn't truely "free", because they do charge you for certain insurance companies, such as GHI, BCBS, Medicare, etc., although a very, very low fee.
OfficeAlly.com is truely free, and they seem to be better organized.  I'm very happy with the services provided by OfficeAlly.com.  I do not use their billing software, though.  I simply generate a print image file and upload to their website.

Both www.OfficeAlly.com and www.FreeClaims.com allow you to submit claims electronically.
You generate a print image file with your billing software, and then upload it.
www.FreeClaims.com isn’t truly “free”, because they charge you a small (very small) fee for certain insurance companies such as GHI, BCBS, Medicare, etc.
www.OfficeAlly.com is truly free.  I’ve been using Office Ally for a while now, and I’m happy with their services.  They seem to be more organized and better ran.