Zoho Invoice - 100% free online invoicing software for small businesses.
Ledger-cli.org - Ledger is a powerful, double-entry accounting system that is accessed from the UNIX command-line.
Monzia - Monzia can help you save money, relieve stress and make time for the fun things in life.
Grisbi - Accounting for everyone !
Kamerge - Kamerge simplifies & systemizes the key processes of your business.
Toshl - See your expenses in beautiful and informative graphs. Save with budgets and monitor your income.