FreshBooks doesn't offer a free version of it's software FreshBooks but they do offer a trial period where you can try FreshBooks for free for a certain amount of time and then pay for it if you decide you like it.
If you don't pay for it then you won't be able to use the free trial anymore but you may be able to find a free alternative to Freshbooks software.
Even the paid version of FreshBooks is not that expensive and well worth it.