The Idolm@ster One For All is a simulation/rhythm game released for Playstation 3 which is a sequel to The Idolm@ster 2. Unlike it's predecessor One For All now lets you be the producer for all 13 idols from 765 Production.
One For All features a lot more freedom to how you manage your idols each week, rather than having 3 timeslots available to fill you are now able to participate in lessons, view communication events, visit the shops and change songs/outfits freely with time only passing when you choose 1 stage or promotion event to tackle each week.
Each season in the game is split up into a block of 12 weeks, inside of which you'll be given a task you'll need to complete prior to the end of the season (such as completing 5 festivals, or getting a certain score during a stage performance). If you successfully do so you'll increase your producer rank and gradually be able to produce more idols.
Idols now gain experience from stage events in addition to their usual Dance, Visual and Vocal stats from lessons. When they level up you gain SP to spend on their skill tree which gives benefits ranging from increased stats to abilities for stage performances. Idols also have their own individual rank system which determines what stage events and skills you have access to, you increase this by completing Rank Up Festivals.
Stage performances have received a number of changes, mostly regarding the burst system. With the right skills your idols can now counter rival bursts or use Duo/Trio bursts which let 2 or 3 idols join in, giving you a boost.