The aptly titled ASCIIvania by gharding3 contains one of the more novel mechanics in an already burgeoning genre of word games. It's a pseudo-linear 2D platformer where you control various letters that can unlock barriers of text by spelling words.
Initially you'll be asked to enter your name. Using your first initial, you'll wander around collecting other letters that you can transform into. Say you come across a narrow passage blocked by the letters "EFT" and you'll need to have acquired "L" to gain access.
Things get a lot more interesting when words are cobbled together in more condensed arrangements that can be dismantled bit by bit by forming smaller words around them with your alphabet-based avatar.
It's a simple game devoid of story, combat or fancy graphics, but its arresting mix of wordplay and exploration is superb.