Quasi-gestalt (3.5e Variant Rule)

Quasi-gestalt
There are various systems which offer a level cap to growth, such as E6, E10, E20, and others. Once the cap is reached, it offers minor benefits but no change in classes or growth beyond what feats offer. However with quasi-gestalt rules, full horizontal growth is possible by effectively transforming you into a gestalt character late-game.

Once the level cap is reached, the next level you obtain is instead a gestalt level as if you were level 1 again. Taking for example an E6 game, a Wizard 6 reaches a new level and chooses Fighter. His 1st class level is gestalted with Fighter, giving him Good BAB, d10, a bonus fighter feat, and Good Fortitude (from fighter) while retaining spellcasting, Scribe Scroll, and a Good Will save from wizard. This continues, possibly endless times becoming double, triple, quadruple, and further gestalted. Taken to its extreme, all characters could potentially end up with all good saves, good BAB, d12 HD, and all class features from all sorts of classes without any actual vertical growth at all.