find_all_commits_from_author.rb

author = "joe"
repos = Dir["**/.git/"].map {|r| r.gsub('.git','') }
stats = repos.map {|r| [r, `cd #{r} && git log --author=#{author} --format=format:"%ad %s" --date=short`.split("\n")]}
commits = stats.flat_map {|r, cs| cs.map {|c| d,cm = c.match(/(\d{4}-\d{2}-\d{2}) (.*)/).to_a[1..2]; [d, File.basename(r), cm]}}
str = commits.sort_by(&:first).map {|c| c.join("\t")}.join("\n")
File.open("commits_#{author}.txt", 'w') {|f| f.puts str}

Run this script in a directory which contains all your Git projects (in arbitrary subfolders).
It will search for all commits from the specified author and sort them by date.
Good to refresh your memory sometimes ;)