Maybe Kyoto Shogi? It has some funny/remarkable changes from Shogi:
"In kyoto, there is no promotion: at the conclusion of every move the piece that moved must be reversed."
It is also played on 5x5, but with 2x5 pieces. Here is the site: http://www.drjochum.de/ (click on the link)
I haven't played it, I leave it to the expert Shogi players to judge :) but looks fun to me.
I found some larger Shogi Variants but to me they look to slow for a turn-based site.
(скрий) Губите ли игри поради изтекло време? Платените членове могат да активират Автоматична Ваканция, която се активизира автоматично за да предотврати загуба поради изтекло време. (pauloaguia) (покажи всички подсказки)