Their "About" page:
https://secure.actblue.com/about .
Known: They have successfully solicited donations from me for causes I consider critical, and their site says that the money they raise goes only to the specific causes for which it's solicited. E.g., I just got an email soliciting funds to fight the new indefinite detention law and implying that the funds would help finance a lawsuit brought by Chris Hedges et al. challenging the law.
Unknown: Their site says they raise money for Democrats (in general). Which nationally-known Dems have they raised money for? Is there any connection between this organization and the Democratic Party?