I've never done any leatherworking myself (too intimidated at the prospect of messing up and wasting some poor animal's hide), but I have huge respect for those who do it well. If you're thinking about giving it a try, watch these videos for some ideas on tooling.

Home Made Leather Splitter by Canal de Aldo08101979

Making a leather edge burnishing tool by Richard Black

Handmade Tools - Homemade Tools - Leather Tools by Bruce Cheaney

Handmade leather craft tool by Mr. Tolly (AKA: fatmantolly)

Stitching Pony Leather Crafting Build by Crafted