Modular Icons which is part of the Native Instruments Play Series does sound modular. I Love the sounds and feel of this library. Built-in sequencer is really easy to use and you can apply it to pitch, velocity and the macros.
The play series is mostly about blending two layers and create some very useful sounds with minimalistic user interface. The sound browser is easy to use and the extra options are very useful. For example you can map the layers to different ranges on the key board and so layer A can be triggered by the lower part of the key board while layer B is triggered by the upper part of the keyboard and they can overlap as well.