The other one i linked to Allice earlier, Wagic The Homebrew (or WTH), i used to be a Dev there aswell but i kind of got sidetracked and didn't really pick it up again afterwards but the project continued none the less. It started as a Sony PSP version off the game in which you could play against A.I. (Computers) but quickly formed into a PC and Linux version because of populair demand. You can buy boosters in game, build decks, play text based campaigns etc. etc.
It's actually really good, definatly if you want to get started again because easy mode works perfectly (there are no tutorials on Magic itself in it though but the card text kind of explains it and the system auto blocks most illegal targets etc/), the only thing is that you don't have card images when you download it, you have to manually add it by downloading the full packs from the forum (or downloading a premade thing from the piratebay or any other public tracker).
The only things it didn't do at the time of my departure was follow the exact tournement card resolving rules (as in you play a spell, your opponent does aswell, some abilites activate and you play something again), they didn't 100% follow the rules all the time but that was because of the semi-flexible engine not being bendable enough. Good chance they solved 99% of it yet i highly doubt they added the extreme tournament rules already (that's hard to even remember so just imagine how hard it is to code them correctly :P).
Link: Wagic · Wololo.net
(@Allice check out that link instead, the one i gave you earlier was an outdated version).
I'm also looking into online versions at the moment, we could play online by exchanging info in the IRC channel and, if the TI MTG community grows, maybe host a tournament giving away a VIP/Temp Seedbox /Whatever to the people in 1st place and the runner ups.
Pretty much depends on what i can find, how many people would enjoy playing against each other and ofcourse if I can find sponsors ^_^