Two mobile-mining projects like #pi that are still in early stage and something to look out for:
1. Delta Coin: This is a super-early stage project with userbase under 80K and the mining rate is crazy high right now. The mining app "Delta" can be downloaded from the website Delta.kim (just search Delta.kim on Google) in the form of an apk. The userbase is growing at an exponential pace ever since the advent of Pi coin, so this is one of the projects you won't want to miss on if you intend to be early. They have a whitepaper that looks quite promising, at least for now.
Use my referral code (App calls it DID) for 33.33% mining boost: D9C1NK1C7H0C4
2. #BlockDAG : They recently fundraised around $200M for their project presale (Currently in Phase 27 of presale) and plan to be listed on 10 CEX exchanges this year itself after its Blockchain is developed (When it hits Phase 50 of presale). They have a mining app called BlockDAG X1 Miner that's available as an apk on their website "Blockdag.network" and is currently not available on Play Store (will be available soon). They also plan to roll out miners X10, X30, and X100 this March that accelerates mining several times over. However, I'd say just sticking with free-mining using your mobile phone BlockDAG X1 is good enough. You can also use multiple phones to mine this.
Use my referral code for 20% mining boost: A4qlM83a