Magic Online is the full-fledged digital version of Magic: The Gathering. The beta for the new version of it entered open beta last month, but only for a brief period. If you missed it or just want more, it's now in "wide" beta, which is to say anyone can try it, and for an "extended" period of time.
The official word is this newer beta has "new and updated features", though it's not clear exactly which and how. In any case, it should be worth a look. Hit the source to download.