This visa can be obtained by almost all nationalities at all borders and international airports.
The cost is U$50 for most nationalities. Americans and Irish are U$100.
This visa will allow one re entry if you stay within East Africa and within 30 days of when the visa was issued, so for example if you climb Kilimanjaro and then travel to Nairobi to do a trip that commences in Kenya and later travels to Tanzania you can then usually re enter on the same visa.
Hong Kong, Singaporean, South African and most other African nationals are visa free.
The Tanzania visa is a full page visa