Sliding pipe, wood splitter.

This wood splitter looks pretty simple. The pipe, with a heavy steel end cap, is slid up and down in a hammering action. The rope limits the length of stroke.

This one was at a thrift store.

looks like a nice simple design, one you could recreate pretty easily with a welder, scrap pipe and old wedge. I'd probably put a little bit of weight on the top of it, but I've been told I'm kind of a big guy.

Yes, the pictures are for all of the welders out there. I would like to see heavier pipe and possibly a sledgehammer head welded to the top.

Stuck wedges are a pain. The lever arm should help.

Smart Splitter - That tool uses a weight to split wood. It is a pretty interesting design. Looks like it is a lot easier than swinging an axe. Amazon also has manual wood splitters similar to the one posted above at a much cheaper price than the smart splitter.

It should be fairly easy to add weight to that splitter without a welder. You could find a pipe that fits over the handle and an appropriate pipe cap. Cut up the pipe lengthwise a bit at the end opposite the pipe cap and clamp it in place. I'm sure someone could get creative from here and use items and tools on hand to create something effective. You could pour metal into the pipe to add more weight at the pipe cap. Zamack 27 - the alloy mentioned in that link has a strength similar to cast iron but melts at a lower temperature than aluminum. I have learned tons of stuff from that forum, some really excellent work happening over there.

Looks like this tool might work well on some straight-grained firewood like spruce or Aspen...not really confident how well it would perform on a gnarly twisted piece of Osage Orange or Beech