Crowdloan is a feature of the Polkadot / Kusama ecosystem. It allows DOT / KSM holders to contribute to projects they back without putting their principal DOT / KSM balance at risk. This is called a lossless crowdloan, in contrast to the previous ICO (initial coin offering) model where the entire contribution is at risk.

In the DOT / KSM crowdloan model, contributors forgo the staking opportunity cost in exchange for earning the new tokens from projects they contribute to. For example, if you have 100 DOT and you decide to contribute the entire 100 DOT to project ABC, your 100 DOT will be locked up for the duration of project’s ABC parachain lease, but it will not be at risk. At the end of the parachain lease (for example 96 weeks), you will get back your 100 DOT. In return for your crowdloan, project ABC will distribute its tokens to you, for example 2000 token ABC at a rate of 20 ABC token per 1 DOT pledged to its project. In this example, at the end of the parachain lease of 96 weeks, you’d get back your original 100 DOT plus the 2000 token ABC.

Polkadot crowdloan – batch 1

#	Project	Reward Ratio	Total Tokens	Lease Period	Bonus Link
1	Acala (ACA)	12 ACA : 1 DOT	1 Bil	96 w	Extra 5% referral bonus +Extra 5% early bird bonus (end 11/8 1AM PST)
2	Astar (ASTR)	430 ASTR : 1 DOT	7 Bil	96 w	Extra 1% referral bonus +Extra 20% early bird bonus (end 11/18) +Extra 10% SDN supporter bonus
3	Parallel Heiko (PARA)	25+ PARA : 1 DOT		96 w	Extra 5% referral bonus +Extra 40% early bird bonus (end 11/13) +NFT for 1000 random contributors
4	Moonbeam (GLMR)	13 GLMR : 1 DOT		96 w	Extra 5% PARA referral bonus
5	Manta (MANTA)	188 MANTA : 1 DOT		96 w	Extra 10% PARA referral bonus +Extra 10% early bird bonus + NFT

Reference: https://dotmarketcap.com/auction/polkadot