I already donated a lot of money to https://thewaterproject.org/donate-bitcoin and what I like about their service is that they are accepting 4 other Alt coins for donations too. 
I got some FREE fork coins after the Bitcoin fork and I donated a lot of the BCash that I received to their water projects.
I see your site wants you to login with Social media accounts and that might be an option that some people would want to avoid. Staying anonymous, helps people to prevent situations where information about them might get into the wrong hands and that they might get bombarded with fake sites that wants "donations" for fake projects.
I got some FREE fork coins after the Bitcoin fork and I donated a lot of the BCash that I received to their water projects. I see your site wants you to login with Social media accounts and that might be an option that some people would want to avoid. Staying anonymous, helps people to prevent situations where information about them might get into the wrong hands and that they might get bombarded with fake sites that wants "donations" for fake projects.
That's great that you are supporting The Water Project! They are our one of our earliest partners, and we supported three projects with them in Kenya over the years.
For donating other cryptos - GiveTrack has a direct integration with Uphold, and you can donate in now 50 different currencies - both crypto and fiat. Here's a list of all the supported currencies - https://support.uphold.com/hc/en-us/articles/202473803-Supported-currencies
GiveTrack also issues a receipt upon donating, once the transaction is confirmed on the bitcoin network.
You are not required to sign up via social media, it's provided as an option for those who enjoy the ease of that type of registration, but not necessary. You can sign up using an email address instead, and you can easily opt-in to be anonymous to the public, as a setting in your profile. Unfortunately US regulations require that we gather at least some information from a donor.
We are also GDPR compliant, which are the strictest data privacy regulations in the world, so your data is safe.
As a nonprofit ourselves, we've worked very hard to check all the boxes on a resource-constrained budget, and we are proud to offer all these different options, ways to donate, and services to further the use of bitcoin, cryptocurrency, and blockchain technology in the charitable sector.