iPXE (you can use this to chain load other thin OS’s over the internet, nfs, smb, etc..)
Very small, and configurable. Supports some wireless cards.
Basically a zero client. < 1MB.
Windows XP, Vista, 7, 8, embedded, CE, etc…
If you already have a windows device, you can convert it into a thinclient using:
These two support SPICE! For VDI deployment to KVM-QEMU
VDI Blaster http://www.devonit.com/thin-client-solutions/vdi-blaster