There's also Pancake (https://www.pancakeapp.com/), Thrive Solo (http://thrivesolo.com/), Duet (https://duetapp.com/), Invoice Ninja (https://www.invoiceninja.com/), Flowlu (https://www.flowlu.com), Plutio (https://www.plutio.com/), and Freelance Suite (http://freelancesuite.com/), and those are just the ones I've tried.

Highly competed, but few seem to have staying power.