As there is no legal "RocWiki" organization, donations are not tax deductible and can't be made payable to "RocWiki" or anything cool like that, so there's no official donation mechanism. Buy your favorite RocWiki contributor a good beer, coffee, or other drink-of-choice. Generally speaking, the best way you can help the Wiki is by contributing content, photos, profreading, and telling your friends about RocWiki.
If you're looking for a most excellent Linux virtual server, take a look at Linode! That link contains a referral code, which will contribute $20 towards RocWiki's hosting.
After giving generously, give yourself credit on the Talk page.
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