Not long ago Raspberry Pi model B+ was announced. It had several great improvements in layout and GPIO. Other things like processor, RAM capacity remained same. So not long ago Raspberry Pi model A+ was announced and now you can get one for $20. As name implies, improvements are similar to model B+ just it remains without Ethernet and with less USB.
Among improvements we can see a micro SD card slot instead of SD. This gives more compact look and feel. Video and audio now are integrated in to single 3.5mm jack. GPIO port also was expanded from 26 to 40-pin header. Camera and display interfaces remain same. Also there are convenient mounting holes. Its dimensions shrunk to 65 x 56 mm. So if you don’t need Ethernet connectivity but still want Linux powered machine for battery powered projects, Raspberry Pi model A++ is a great choice.