InvoicePlane is a self-hosted open source application for managing your quotes, invoices, clients and payments.

Bitrix24 is a free (for small businesses) social enterprise platform.

Manager is free accounting software for small business. Windows, Mac and Linux.

Active Collab is a web-based project management tool.

FrontAccounting (FA) is a professional web-based Accounting system.

Xero is an accounting software to manage invoicing, bank reconciliation, bookkeeping & more.

Avaza is a beautiful online software suite with modules for Project Management, Timesheets, Expenses & Invoicing. Access from anywhere, with any device.

InvoiceBerry offers online invoicing & expense tracking for small businesses, freelancers and sole traders.

ZipBooks is an online accounting platform.

TimeCamp is an advanced time-tracking app which also offers a variety of reporting, billing, and invoicing features.

Vosae is an invoicing, organizer, contacts app.