Even if you don't use it actively, it periodically saves the state of your windows and tabs (all locally), so you can restore sessions from months and years ago.
SessionBuddy is amazing. It is the only thing I am missing from chrome.
Although it is not open-source, it has customizable exports in a variety of text formats
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Too tired to write more, but if you use chrome check it out.
Even if you don't use it actively, it periodically saves the state of your windows and tabs (all locally), so you can restore sessions from months and years ago.