At the highest level, software companies are measured by the same KPIs as companies in any other industry, which include Revenue, Profits, Stock Price, Market Cap, Earnings Per Share, Price/Earnings ratio, etc.
At the operating level, though, there are industry-specific KPIs.
KPIs for Software Product company include Average Contract Value, Monthly Run Rate, Annual Contract Value, Churn Rate, Leads per Month, Orders Booked per Quarter, Days of Sales Outstandings, etc.
KPIs for Software Services company include Revenue Per Employee, Utilization Rate, Bench Strength, Leads per Month, Orders Booked per Quarter, Manpower Attrition Rate, Days of Sales Outstandings, Defects per Thousand Lines of Code, etc.