Currently testing it with Gossip : https://github.com/ok300/gossip/tree/ok300-powwow-client (cc nostr:npub1acg6thl5psv62405rljzkj8spesceyfz2c32udakc2ak0dmvfeyse9p35c). This lets my Gossip client buy PoW for every event (note, repost, etc). Very rudimentary, but good enough as proof of concept.

There is also a WASM client, which I'm testing on mobile: https://oak-node.net/demo/powwow/

Best would be of course a native mobile app, but haven't found the time to do that yet.