Recently Wizards of the Coast have named and given more attention to the Type 1.5 format, now called Legacy. This development is good for casual and multiplayer games for several reasons.
Especially now that the banned and restricted lists are distinct from the Vintage (Type I) format, Legacy provides a common framework in casual and multiplayer games that allows for nearly anything a player might bring to the table outside the early expensive cards that define Vintage itself, while also not limiting players to only recent sets and mechanics as do the Standard and Extended formats. This ability to bridge divergent card collections has another benefit, in that it encourages exploration of how Magic works on a theoretical level as a whole; the game theory of Magic on a long term scale, without skewing toward one recent trend or powerful mechanic. A good example of reflection on the larger patterns in Magic can be found here, at the useful and interesting Magical Article page/
While on the topic of helpful webtools, the Essential Magic site to which the CPA has a link offers a great forum for both designing and sharing decks, complete with card images for explanation and sample draws to see how a deck will play out. Getting an account is a free process that requires email activation; an example deck from an earlier article on this site can be viewed in the Essential Magic layout here:
Finally, the Legacy format allows players to express their design creativity in ways that are not possible with the limitations of the other formats, in some ways similar to the fun oddities allowed within the Unglued and more recent Unhinged sets. As an example using the above deck, after drawing all the cards in the library one can cast a Burning Wish to fetch an Energy Bolt, a Golden Wish to fetch a Mirari, and finally a Death Wish to go after any number of cards you own, using the Mirari copy to fetch back the actual Death Wish card. This allows for amusing and/or aggravating win conditions like returning all permanents to hands with Upheaval, casting Words of Waste and skipping draws from the Wall of Mulch to have all opponents discards their hands, using a Coffin Purge on Misinformation and Paradigm Shift to return all graveyards to libraries, and gaining control of all cards in all libraries through a Grinning Totem with Karn, Silver Golem due to your infinite mana and Enduring Renewal.
An endgame in which you control every card that you and your opponents began the game with along with any number of cards you own while having infinite mana that can be spent as any color to cast them as many times you like; that is the power of the Legacy format.