Complex sentence: HubSpot's "startup within a startup" program was started in 2008 after a salesperson's evening and weekend project on a partner program became their full-time job and by 2011 it was responsible for 20 percent of HubSpot's revenue.
Split into simpler sentences: HubSpot's "startup within a startup" program was started in 2008 after a salesperson's evening and weekend project on a partner program became their full-time job. By 2011 the partner program was responsible for 20 percent of HubSpot's revenue.