Back in 1988, co-founders Mike Muhney and Pat Sullivan "sat in a 10x10 office for 10 months and laboriously birthed Act!". From such humble beginnings emerged one of the most enduring CRM products in history.
Over the next decade and half the Act! program evolved from a DOS application to Windows, and from a Foxpro architecture to SQL. Sage undertook the monumental task of making this arduous transition from DBF to SQL, and by 2007 released a version built on SQL2005.
This SQL standard would remain in place for another four years until Act! 2010 came out, supporting both SQL 2005 and 2008. Of note, the Act! 2010 version introduced huge changes to the structure of Act!, as Opportunities were promoted to the level of parent table, to match Contacts, Groups, and Companies. This one change dramatically enhanced the capabilities of Opportunities, and changed pipeline management within Act! for years. 
Subsequent years saw fewer dramatic feature changes to the product under Sage's management, until in 2013 Swiftpage took ownership and re-branded it as Act! In May of 2015, Swiftpage made the bold move to transition to a subscription based purchase model, and thereby joined the majority of the CRM industry. This one change made Act! accessible to more businesses as the cost barrier to access was significantly lowered.
You can see an illustration of the Act! historical timeline below. For a historical breakdown of how the product's features evolved over the years, from version to version, please click HERE.