<h1>Proof-of-Activity</h1>
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Proof-of-activity achieves node selection through a combination of the efforts of Proof-of-work miners and Proof-of-stake minters. Firstly, Proof-of-work miners solve a proof-of-work problem, and then each ‘winner’ presents a proposed block (i.e. a ‘template’) to the network. The hash of the proposed block is then used to generate N pseudorandom numbers, which are mapped to the public keys of certain nodes holding coins (i.e. having a stake). These stake holders then sign the block. If some of these stake holders are unavailable, the process repeats through another cycle, and so on until a block is accepted.
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<H1>Strengths</H1>
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The Proof-of-stake minters only become involved after some work has already been done by Proof-of-work miners. So even if a Proof-of-stake miner owns over 50% of all coins, it cannot control creation of blocks on its own. Plus, if N is greater than 1, the minter must consider other minters, too. 
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<h1>Weaknesses</h1>
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The protocol requires continuous data exchange. To reduce traffic, the template does not contain the transaction list, which is only added by the last signer when finalizing the block. If N=3 and only 10% of users are online, proof-of-work miners will need to generate 10 x 10 x 10 = 1000 templates before one of them is signed. But if message size is only 100 bytes, this is insignificant.
Meissa Platform and Delegated Proof-of-activity. The Meissa Platform is a project to connect devices and data centres securely in a decentralized, distributed network by deploying a global virtual ‘supercomputer’ to execute decentralised applications, transfer money and messages between peers, and to share resources.
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Meissa’s consensus algorithm is referred to as Delegated Proof-of-activity, and broadly follows the principles outlined immediately above (see Proof-of-activity). The mining element is referred to as ‘Computative Proof-of-work’, and is designed to be memory intensive and therefore ASIC-resistant (to discourage centralized mining pools). The minting element is referred to as ‘Delegated Proof-of-stake version 2’, and requires the selection of a random set of stakers based on their ownership percentage, who together verify and broadcast the block, and collect block rewards in return. The method allows for consistent block times and near-instant verification. 
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