This is almost becoming a regular occurrence: Newly reunited college-rock legends The Replacements have been confirmed for their second festival appearance in as many days this morning at Boston Calling rolls out the lineup for its Sept. 5-7 extravaganza.

Like OutKast, reunited college-rock legends The Replacements seem content to stick strictly to festivals, the latest of which is the just-announced two-weekend Austin City Limits Music Festival in October, where the ‘Mats will join headliners Eminem, Pearl Jam, Skrillex, Beck and, of course, OutKast on the massive bill.

Coachella’s second weekend is under way now, and The Replacements took the stage tonight for the second of the reunited band’s appearances at the two-weekend fest — and dropped a big surprise on the crowd, as Green Day’ Billie Joe Armstrong joined the ‘Mats for part of the band’s set.

Third time’s the charm? One-half of The Smiths reunited on stage Sunday for the third time in less than a year, as bassist Andy Rourke joined Johnny Marr toward the end of his Lollapalooza Brazil set to perform their former band’s classic “How Soon Is Now?”

Last night, Hunters & Collectors brought its 2014 tour to Sydney for the first of two club dates at the Enmore Theatre, and treated fans to an encore surprise, inviting Peter Garrett and Jim Moginie of Midnight Oil onstage to help blast through a cover of The Saints’ “Know Your Product.”

It’s perhaps not surprising that The Replacements’ reunion has been a ramshackle affair, with the band playing three festivals last year, and, at this point, slated to perform five more times this spring and summer. To hear bassist Tommy Stinson tell it, that may continue for a while.

The Replacements reunion returns to Canada — where it began — this summer with a just-announced appearance at the Osheaga Music Festival in Montreal, just the latest in what continues to be a festival-only affair for the reunited ‘Mats. The band joins Nick Cave & The Bad Seeds at the Aug. 1-3 festival.