Webmention is a W3C Proposed Recommendation https://www.w3.org/blog/news/archives/5916
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aaronpk_tv
Alphabet graveyard: A for Answers, B for Base, C for Code, D for Dodgeball, E for Etherpad, F for Friend Connect, G for Gears, H for Health, I for iGoogle, J for Jaiku, K for Knol, L for Latitude, M for Meebo, N for Nexus Q, O for Orkut, P for Picasa, Q for Quickoffice, R for Reader, S for Sidewiki, T for Talk, U for University Search, V for Video, W for Wave, X for Google X.
I’m sure Google will discontinue a service starting with ‘Y’ and ‘Z’ soon. Rest in peace.