I use my own in house software to track my time, invoice, track assets, procurement and calculate income tax and GST. Jobs are listed and can be ordered by urgency (the next todo), importance or last updated. They can be filtered by the client as in the case of the figure below:
Pie charts of the percentage of chargeable time I spend on which job are generated by my end of week report, that tells me how many hours I have spend on each job. time is reported as Chargeable, Downtime and total.
Invoices drag text from my updates or notes that have been recorded for the job over the week (or other period I wish to invoice for). These notes populate the invoice record and the number of hours. I enter the charge rate, and click a button to generate the PDF invoice.