Monero

It depends what country you're in. In the US, you get a tax cut for charitable donations. It has to be donated to a nonprofit.

So say you buy xmr for $100 and donate it when it's a value of $150. Normally if you sold it, you'd owe capital gains taxes on the $50 profit. Since you donated it, you have a write off for the full amount of the value at the time of the donation, so your capital gains at the end of the year get taxed their value minus the charitable donation, which is $150 in this example.

If the dev is running a nonprofit, they don't owe taxes. If they aren't, the entire amount is taxed as income, plus capital gains when they sell if they sell later for a profit.

If the dev isn't running a nonprofit, and you donate to them, it isn't a charitable donation, it's a gift. You'll owe taxes on the capital gain (taxes on $50 in the above example) and you have a lifetime gift limit that you can gift with no tax liability, but once you reach that limit you'll owe taxes on all subsequent gifts. I believe this limit is $10,000,000.

Again. This is for the US. I don't know what country you live in. Some countries tax nonprofits, don't allow you to write off charity, have no gift taxes, some even have no capital gains taxes. Some countries the recipient of a gift pays tax, some the giver, in the US it's the giver.