U-he offers Zebralette for free. Zebralette is the small brother/sister of Zebra 2. Actually, Zebralette is one of Zebra2's oscillators packed into a simple framework. Zebralette also has two LFOs (one per voice, one global), a multi-stage envelope and three on-board effects (chorus, EQ, delay). And now it's 64 bit als well. Thanks, Urs!
Update: Nice Video with Urs explaining Zebralette.