I practice with Rissho Kosei Kai which is a Lotus Sutra -centered "Ekayana" sect of Buddhism from Japan. RKK is obviously Nichiren influenced but does not consider itself to be a Nichiren school (so I guess this is the best category on this board).
The main practice of RKK is chanting portions of the chapters of the Lotus Sutra (in RKK we chant these in the language of our understanding - in my case English as the point is to understand what you are chanting - chanting helps you to focus and internalize) as well as O-Daimoku (basically the title of the Lotus Sutra) as well as Ti Sarana (Taking the Three Refuges). Our daily liturgy called Kyoten is most similar to that of Nichiren Shu. A practice unique to RKK is hoza which is a form of group counselling which uses the foundational teachings of Buddhism (the Four Noble Truths and Eightfold Path but also the Six Paramitas) as a framework to examine our everyday life problems and issues through the lens of Buddhadharma.
We consider ourselves to be mainstream Buddhism and engage in a lot of interfaith and peace activities. Many of us also practice sitting meditation as a part of our daily practice. RKK is very ecumenical and believes that there are "84,000" paths to enlightenment so we do not suffer from the "one true school" syndrome - folks should gravitate to the school of Buddhadharma which resonates best for them.
Here are some links to RKK websites:
http://www.rk-world.org/home.aspx
http://www.buddhistcenter-rkina.org/
Here is a link to the online text (and pdf download) for "Buddhism for Today" which is the RKK basic text used for study along with the Lotus Sutra:
http://www.rk-world.org/publications/bu ... y_toc.aspx


I too regard Rissho Kosei Kai as a Lotus Sutra School, you really stick with the sutra which I admire. I've enjoyed reading the magazine as well. In fact we had a discussion about how many followers of Lotus Sutra schools there are in Japan, and the figure someone posted omitted the 'new' religions, but really I see Rissho as totally mainstream.