This is not for summer prime-time travel but the prices are pretty good if you have plans. You must book before April 19 for travel April 24-June 20. Blackout days and other restrictions vary by route. You can find the details here.
And here are some sample one-way prices from Logan International Airport:
$46 to Nantucket; $49 to Newark, NJ; $60 to Baltimore, Pittsburgh, Washington, DC (Dulles and Reagan), New York (JFK); $90 to Raleigh-Durham; $95 to Chicago; $105 to Jacksonville, Fla.; $120 to Denver and Fort Lauderdale, Fla.; $130 to Orlando, Fla, San Francisco, and Phoenix; $140 to San Jose, Calif., and Austin; $147 to Bermuda; $170 to Portland, Ore., and Los Angeles; $179 to Santo Domingo and Santiago in the Dominican Republic.