We're a lot of different assemblies. We have no central executive committee. All decisions are made within our assemblies by the consensus of those participating in those specific assemblies.
People can join or participate in multiple assemblies (and leave them) at will, while Party Members are automatically assumed to be members of certain core party assemblies. Party Members are also automatically a member of their own local constituency assembly. Constituency assemblies are solely responsible for selection of all candidates for election - though they are supported in that labour by the open-membership Electoral Society (which also governs all internal elections in the party).
We're an open party, so "Party Members" are a different group to "Party Participants": Party Participants are people who participate in the party but don't pay a subscription. Some of these people are even members of other political parties.
All of our assemblies have a specific goal or collectively represent a particular community. Assemblies can be single-issue. Single-issue and narrow-focus assemblies are often members of other assemblies. Each assembly has the sole responsibility for generating consensus in a certain way, or doing a certain type of work. You can read more about assemblies here.
We also have party officers. Party officers are either elected or appointed; for example the Party Treasurer is appointed by the general secretary, as is the nominations officer. Meanwhile all assembly secretaries are elected by the consensus of their specific assemblies. Party officers do not make decisions except where those decisions concur with Party Consensus, and they can be removed if they act without consensus very easily. All decisionmaking is reserved to the Participants and Membership through the expressed consensus of individual or collaborating assemblies.
We are a volunteer party and currently have no paid staff. We only accept donations under £500 from individuals - though organisations can donate larger sums if the Party Membership agrees to the specific donation from the specific source.