## 2 Theoretical Framework  
### Start-Up Accelerators  
The concept of start-up acceleration emerged in the US with the creation of the well-known Y Combinator (2005) and Techstars (2006). They proposed what has become a very successful model for identifying innovative start-ups, supporting their rapid growth by providing seed capital in exchange for equity stakes in the companies, training, mentoring and advice on key aspects over a very short period of time, ranging from 3 to 6 months. As a result, internationally known companies such as Airbnb and Dropbox emerged and started to draw attention from more traditional venture capitalists. Almost as soon as the first accelerators appeared, first in the United States and then in Europe, many researchers began to study this new phenomenon. [PERSON] (2006), and later [PERSON] (2011), were among the first researchers to point out the defining characteristics of the accelerators:  
1. They offer programmes that are in principle open to all, but are nevertheless highly selective (2012).
2. They provide training and mentoring for a limited time (typically 3-6 months) (2013) to connect start-ups with investment, unlike incubators that provide offices, workspaces, training services, mentoring and funding in the form of public subsidies during the first years of the companies' life (2019).
3. They provide seed capital (typically between $18,000 and $25,000) usually in exchange for equity (typically 4-8%) (2014).
4. They support start-ups grouped in cohorts or batches to provide training in an efficient way, promote peer learning and generate a competitive and high-demanding environment.
5. The programme finishes with a graduation event or demo day (2017).  
From an investor perspective, early acceleration programmes were funded by venture capitalists who provided seed capital, debt or convertible notes in exchange for non-controlling minority stakes in the start-ups (2016; 2015). This implied that the accelerators' main source of revenue came from the sale of these stakes in subsequent investment rounds, with some accelerators also charging back a fee for participating in the acceleration programme from the capital provided. For this reason, accelerators were very selective and only accepted start-ups with high growth potential that could scale or fail quickly, thereby minimising the risks of the investment made.  
This first model, driven by venture capitalists and business angels, whose objective was to make profits quickly spread around the world, reaching more than 2000 programmes globally with a wide variety of interests as many organisations felt that the accelerator format could be adapted to their own purposes (2016; 2017). So other types of accelerators emerged with different aims: (1) accelerators driven by governments and public institutions seeking to strengthen entrepreneurial activity in their regions or solve social and environmental challenges; (2) corporations seeking to attract knowledge and innovative solutions; (3) not-for-profits interested in supporting companies with a social impact or working in a particular sector related to their social purpose; and (4) accelerators that organise acceleration programmes financed by external funds (public or private) and are therefore free of charge for the participating start-ups. In these cases, the accelerators do not invest in their portfolio of start-ups or are relatively interested in the possible income that can be obtained from the sales of their shares, because they prioritise other types of objectives, such as attracting talent, corporate image, transferring knowledge to society, improving certain social objectives, etc. [27]. Banka [28] presents an updated review of the state of the art on start-up accelerators available in the Scopus base and suggests future research lines.  
The accelerator observed during the course of this research, IoT Tribe, is equity-free, typically funding its accelerator programmes through a blend of public and corporate sources.